Google's search algorithm has a significant impact on the fortunes of businesses all over the world. It is widely known there are over 200 factors that the algorithm looks at when it decides where to rank a page in a search result.
Here we reveal the complete list of Google's ranking factors. Some are proven, while others are widely accepted as being true even if not proven. Many are speculative, while some spark debate and controversy in the SEO community.
They're all here, so you can decide.
Matt Cutts, Google’s former head of web spam, said in 2010 there is not much difference between a six-month-old and one-year-old domain. That shows two things: domain age is a factor; but it is of limited importance.
Google highlights keywords when you do a search by making them bold, so they do recognize them as important. However, while still relevant, this is less of a factor than it used to be.
Despite the point above, having a keyword as the first word in a domain can help. It should give you a small benefit over competitors who don't.
This one comes from a Google patent. The patent essentially says that valuable domains are paid for in advance, so a domain with an expiry date several years into the future "can be" used as a positive ranking factor.
Moz is one of the most widely respected SEO authorities in the world. In 2011 it said including a keyword in a subdomain can help with rankings, i.e. keyword.yourwebsite.com
Many experts believe Google looks at the history of a domain, looking for the number of owners it has had. Lots of different owners could result in links to the domain being negated.
Exact match domains are an important positive factor, but they come with a health warning. In 2012 Google updated the algorithm and Matt Cutts explicitly stated that exact match domains with low quality websites would be penalized.
This one was discussed by Matt Cutts way back in 2006. He described domains with whois privacy enabled as being "relatively unusual". He went on to say this does not automatically penalize a website, but it helps to build up an overall picture, which could negatively impact rankings.
This one is common sense - if Google has discovered that a domain owner is a spammer, it will suspect other websites belonging to that owner too.
This is for TLDs like .ca, .co.uk, .au, etc. There are two sides to this coin: country specific TLDs do help with rankings in the relevant country; however, they do not rank well outside that country.
The title tag of a page is important, so including the keyword does help. Many experts believe its importance is second only to the actual content on the page.
We go back to Moz research for this one: it found that pages that have title tags with a keyword at the start do better than those with keywords in the middle or at the end.
This is less important now than it used to be, probably because it was abused. However, having a keyword in the description tag can still help.
H1 tags are regarded by many as being almost as important as a title tag. There is also research that shows that having keywords in H1 tags can boost results.
Keywords that are used more frequently on a page than any other keyword are thought to be used as a relevancy signal by Google.
SEO experts have long suspected that longer content ranks better than short. This is backed up by some research, including research by SERPIQ. It found that content with high word counts had improved rankings.
This used to be more important than it is now, which led to keyword stuffing. Google changed the algorithm so it could spot this, and now penalizes sites when identified. However, having a natural keyword density does still help.
Google uses LSI keywords for two purposes: to properly understand the page so it knows, for example, the difference between the fruit and the company when Apple/apple is used on a page; and as a quality signal, i.e. pages that have LSI keywords are higher quality than those that don't.
There is speculation that including LSI keywords in title and/or description tags could help. It is logical that Google would use the content of these tags in the same way that it uses the content on the page.
Google has talked about the importance of page loading speed for years. In 2010 it published a blog post saying it was obsessed with speed. It even makes free tools for website owners to help them improve the speed of their sites. Speed matters.
Duplicate content, even if the original version is on the same site, will harm your ranking. In fact, it can even spot content that has been slightly modified.
To avoid duplicate content penalties, Google recommends the use of canonical tags. It probably therefore, treats positively sites that take this advice and use the tag properly.
When Google looks at the HTML of a webpage it can only estimate loading speeds. It is good at this, but it is not 100 percent accurate. It is widely thought it may use data from its Chrome browser to give it real-world information on a page's speed.
Optimized images help Google determine the relevancy of a page. This includes the filename and alt text, but can also include the image title, description and caption.
In 2010 Google released the Caffeine update to its algorithm. The effect of this was to give greater priority to recently updated content. It even includes the date the content was published in search result pages. For many searches, fresh content has the edge over older posts.
Google regards updated content as being fresh, but the size of the update is important. Changing the odd word is therefore not going to help as much as a significant edit that removes, changes or adds sections.
Google also looks at how often the page has been updated, and the frequency of those updates, since it was first published.
Most SEO experts believe it is important to include the keyword of the page in the first 100 words of content.
Including a keyword in your H2 and H3 tags is not as important as other factors on the page, but it can still help. There is even some research from Moz that backs this up.
Most keywords are a phrase, and the order of the words in that phrase is important. In general, an exact match for the keyword will rank better. For example, a page optimized for "used car prices" will probably do better for searches using the keyword "used car prices" than a page optimized for "prices of used cars".
SEO experts generally believe it is important to include outbound links on your page, but those outbound links should be to websites Google considers as authoritative.
This one comes from Moz. It believes Google checks the relevancy of pages that you link to. Think of the example mentioned earlier: Apple the company or apple the fruit. If you link to pages with apple cooking recipes, it helps Google understand your page is about the fruit.
It is not exactly clear how important spelling and grammar is to Google's algorithm, but it is probably used as a quality signal for the page.
Google prioritizes original content - it even has a Supplemental Index for duplicate or similar content. It regards this index as less important. At the very least, original content will rank higher than scraped or copied content.
Supplementary content is additional content on a page that is helpful to the user. An example that Google uses is recipe sites. Good supplementary content includes links to save the recipe, options to change the serving size, ratings, and links to similar recipes. Google regards supplementary content as a quality indicator.
Having too many outbound links on a page, particularly those that are dofollow, can damage rankings.
Many experts believe Google uses the inclusion of multimedia content on a page (videos, images, podcasts, etc) as a quality signal.
A high number of internal links on a page tells Google that you think this is an important page on your website.
Pages within a website have differing authority levels. Therefore, the authority of links from those pages differs too.
A broken link is a hint to Google the website might be neglected or even abandoned. It has said that it therefore uses this as a quality signal.
How Google uses readability ratings for your content is a debated topic. It does check this though – in fact for a while it displayed reading level info in its results. Most people believe writing for a basic reading level is best because it reaches the widest possible audience, but this is not certain.
Affiliate links are a normal and legitimate part of the architecture of the internet, so are unlikely to cause a problem when used reasonably. Where it might be an issue is if you have too many. Google is always on the hunt for thin sites that are more about affiliate links than content.
HTML errors are a sign of a poor quality site so are likely to hurt rankings. The situation is not as clear with W3C validation. Some experts believe it is very important, while others think you will be okay so long as your site loads properly.
A page on a high authority domain will rank higher than a page on a domain with a lower authority level.
PageRank is a score Google gives the pages on your site, as determined by an algorithm. Its exact impact on search results is not entirely known, but most people believe a higher PageRank on a page will give it a better chance in search than pages with a lower PageRank.
Really long URLs can negatively impact on search rankings. This theory has been backed up with research, including by the widely respected Search Engine Journal.
It is widely believed that pages that are far away from the homepage do not rank as well as pages that are closer.
Google has filed a patent to cover editorial opinion on search results. This means human editors checking the algorithm's results. If and when they plan to start doing this (and if they already do) is not known.
Pages benefit by being in a relevant category over pages in not-as-relevant categories.
This one is specific to WordPress websites, and comes specifically from Yoast, the publisher of popular SEO plugins for WordPress. Yoast says content connected through tags is a relevancy signal.
An example is www.yourwebsite.com/keyword.
Google uses the categories shown in a URL string to get a better understanding of what the page is about. For example, www.yourwebsite.com/category/keyword - it looks at both the "category" part and the "keyword" part.
Most SEO experts believe that citing sources and references, where relevant, is a quality signal to Google.
Google has always told website owners to create content that is helpful to visitors. Bullet point lists and numbered lists make a page easier to read, so it is possible Google regards them as a positive factor.
Google looks at sitemaps - it even asks you to upload them to your Search Console. It is therefore thought the order of a page in a sitemap might be important.
Too many outbound links on a page is distracting for users. Google has highlighted this as an issue, so probably uses it as a ranking factor.
A page that ranks for several keywords will probably do better in search than a page that ranks for just one, or a few.
Content freshness has already been mentioned, i.e. Google doesn't like old content. It does appear to like old pages though, but only if they have regularly updated and relevant content.
Google believes high quality pages make the main content visible to the visitor immediately. This is likely to be a ranking factor.
Parked domains used to rank surprisingly well in search results, but an update on the Google algorithm in 2011 changed this. Now they are much less visible.
Google has published quite a bit about thin affiliate sites and how they offer a poor user experience. It therefore prioritizes websites that deliver real value, are useful, or offer unique insights.
Google is seeking out any sites that don't contain unique or helpful information, particularly in the case of poorly designed affiliate sites.
Google has stated that there should an "appropriate amount" of information on your contact page. It doesn’t go further than that, so most people work on the assumption that more is probably better.
Domain trust is very important to Google so it is one of the most important ranking factors on this list. It measures this by a method referred to as TrustRank. Basically it is a measurement of the quantity of links between your website and one of the web's very high authority sites.
A site that is put together well is easier to understand both for the visitor, and for Google. Good site architecture probably, therefore, helps with your search rankings.
We have already mentioned page freshness, but site freshness is important too. This means sites that are updated regularly, particularly with new content.
This is a small ranking factor, but it is believed to be considered. For example, having a small number of pages can be one indicator of a thin affiliate site.
Including a sitemap on your website helps Google index the pages properly.
Server problems that result in major downtime for your site can negatively impact on your rankings. In some cases you might even be taken out of the index. Repeated or prolonged downtime for site maintenance is also potentially damaging.
The location of your server is believed to be important, particularly for location-related searches. For example, Google will probably regard a website hosted on a local server to be more relevant to a user than one on a server on the other side of the world.
Google likes SSL certificates. In fact it uses them on its own websites. It now wants SSL certificates used "everywhere on the web". As a result it now uses HTTPS (which shows a site has an SSL certificate) as a ranking factor.
Privacy Pages and Terms and Conditions / Terms of Service pages are a signal of quality and trustworthiness.
Most people are aware of the dangers of duplicated page content, but duplicated meta information can be just as damaging. In fact it can impact all the pages on your website.
Breadcrumbs help users understand at a glance where they are on your website. Many experts, including Search Engine Journal, believe Google uses them for the same reason, so they might be used as a ranking factor too.
In simple terms, websites not optimized for mobile devices are penalized in mobile search.
YouTube is not the only video sharing website on the internet, but most people believe it gets priority in search results. The opinion is backed up by some research. For example, Search Engine Land found that traffic to YouTube Increased after Google's Panda update in 2011.
It is thought Google makes this assessment in a number of different ways. This includes how long visitors spend on your website and how many pages they visit. What it wants to see is sites that are easy to use and navigate.
Some experts believe using Google Analytics and Google Search Console can help with your ranking. The theory is that it gives Google better data, so helps it build a more accurate picture.
Google looks at reviews of your business and website, including on sites like Yelp.com. It has also corrected a problem found in 2010 where negative reviews could actually boost a website because of the backlinks generated. It can now differentiate between good reviews and bad.
Links from domains that have been around a long time are probably better than links from newer websites.
Generally, more domains linking to your website means you will have a better rank in search. This is considered to be a crucial ranking factor, and research from Moz backs this up. However, it specifically applies to the number of root domains.
Getting links from separate Class C IPs demonstrates to Google a wide range of websites have links to your site, which is good.
This is not as important as the number of root domains, but the number of linking pages is still a ranking factor.
Google treats alt tags on images as being like anchor text, so they are a ranking factor.
There is some controversy over this one as Matt Cutts has said TLD doesn't matter. That means a link from a .gov website is treated exactly the same as a link from a .com. However, many SEO experts still believe the algorithm looks at .edu and .gov more favourably.
Another thing that is important is the authority of the page that is linking to you, as determined by PageRank.
The PageRank of the linking domain is also thought to be a factor. For example, a link from a website with a higher PageRank is probably worth more than one with a lower PageRank, even if the PageRank of the linking page is exactly the same.
Links from other websites and pages that rank for the same keyword is a positive ranking factor.
It is believed the number of social shares on a linking page increases the value of the link.
An example of a bad neighbourhood link is a link from a link farm. These links are likely to hurt your site.
Guest posting is a commonly used and legitimate marketing and SEO tool. However, the value of links generated through guest posting is debated. At the very least, a link in an author bio part of a page is probably worth less than a link within the content itself.
The number of links that a linking page's website has increases the value of the link passed to you.
This is a hotly debated area of SEO. The theory is Google doesn't follow them, so doesn't count them. But it has also stated that "in general" it doesn't follow them. That would indicate that sometimes it does! A natural link profile has a combination of both follow and nofollow links, so that is probably what you should aim for.
A natural link profile will include links from a range of different sources. If they all come from the same sort of location though, such as all from blog comments, it can look unnatural.
We all know that not all links are the same, and it is thought Google gives links that look sponsored lower value than those that don't. Using anchor text or words close to the link helps Google identify this: words like "Sponsored by" or "Sponsored Link".
These are links located within the content of the page. Most experts believe they are better than any other form of link, regardless of the website they come from.
Google released a video in 2011 which said that too many 301 redirects can negatively affect the PageRank of a page.
This used to be regarded as a critical ranking factor, but that led to it being abused. It is probably less important now, but it still helps Google determine relevancy - when used properly.
This is likely to be less important than the anchor text of external links, but it still plays a small ranking role.
The title of a link is a ranking factor, but a very minor one.
Links from country TLDs probably help with your rankings, but only in the country where the link comes from.
Links at the start of a page, or close to the beginning of content, are better than links closer to the end - although only slightly.
Links in content are more valuable than links elsewhere on a page, such as in the footer or in a sidebar.
The relevancy of a website linking to yours is an important ranking factor. If the website is in a similar niche, sector or industry, the link will be worth more than one from a website where the connection is not as clear.
The relevancy of a page is also important. If the page linking to your page has similar content, it will be worth more than one from a page with unrelated content.
As mentioned in a previous point, Google is getting better at determining the sentiment of a link. In other words, it can tell if the link is connected to critical comments, or is a recommendation. It figures this out by looking at the text around the link.
One of the most valuable types of links that you can get is a link from a page whose page title contains the keyword of your page.
A positive link velocity means you are gaining links faster than you are losing them. This will boost your rankings.
Negative link velocity is an indication to Google that your website is becoming less popular, as you are losing more links than you are gaining. It will hurt your ratings.
Top resources on any particular topic are known as hub pages. Links from these pages have long been regarded as quite valuable.
Links from authority websites are better than links from websites that Google does not know or trust as well.
Everyone knows that Wikipedia links are nofollow. However, many SEO experts still think Google looks at these, and they can help you build authority and trust.
Co-occurrence is a term used to describe words that are commonly used close to other words. Google looks at the co-occurrence of words around the text of a link to a page on your site. It helps Google get a better understanding of what the page is about.
This is another one that comes from a Google patent. In the patent, Google states that old links have more value than new links.
It is easy to set up a blog on one of the popular networks, which has led to the creation of a large number of fake sites and blogs. Google therefore regards links from real sites as being more valuable than sites it suspects as fake.
Google's algorithm updates are designed to improve user experience by lower the rank of poor quality sites, and improving the rank of others. Legitimate sites can inadvertently get caught in an update's net, though. Having a natural link profile can help to mitigate this.
Excessive link exchanges will damage your rankings. This is where a site links to another in exchange for a link back.
Google generally knows when a link is generated by the site owner, or by a user on the site. Links generated by the site owner have more value.
In 2013 Matt Cutts said links from 301 redirects are treated exactly the same as other links. Some SEO experts still believe that 301 redirects have slightly less value.
Many people believe that pages using Schema.org microformats rank better than those that don't. One theory for this is that markup protocols like this result in higher click through rates. In other words, it might not be the microformats that directly give the boost, but rather the resulting improvement in click through rate.
Many experts believe that Google attaches a small amount of extra trust to websites listed in the DMOZ directory.
Sites with a high TrustRank will pass on more TrustRank juice to you when they give you a link than a site with a low TrustRank.
When a page links to yours, that page's PageRank is passed to yours. However, that PageRank is distributed to all the links on the page. So if the linking page has lots of outbound link, less PageRank will be passed to you.
Putting links in forum profiles was (and still is) a favorite tactic of spammers. It is therefore likely that Google gives them a lot less value than many other types of link.
A page with a high word count is a more valuable link than a page with not much text content.
Links on pages with well-written content, proper spelling, correct grammar, and multimedia, are more valuable than links on pages with poor quality content.
Site-wide links occur when, for example, the link to your page is in the footer. There are therefore lots of them, but in 2012 Matt Cutts confirmed Google only counts them as one.
High organic click through rates on a keyword are thought to boost rankings, but probably only for that keyword.
High click through rates for all the keywords that the page ranks for is also believed to be a factor.
Bounce rates are the subject of debate in the SEO industry. Some experts believe they don't matter. Others think it is one method that Google uses to check the quality of a page, i.e. high bounce rate equals low quality.
Many people believe that Google analyses direct traffic to websites through its Chrome browser. Sites that get lots of direct traffic, and that users visit frequently, are likely to be regarded as better quality than those that don't.
The fact that visitors come back to your website is thought to be used by Google as an indication of quality.
The Google Panda update in 2011 included search blocking data from the Chrome web browser. This is now probably less of a factor as the blocking feature is no longer available on Chrome.
Information on the bookmarks you have in Chrome is sent back to Google. It is therefore possible that it may use this data as a quality signal when ranking pages.
In 2011, Google confirmed to Search Engine Watch that data from the Google Toolbar is used as a ranking factor. We know that means information on page loading speed and malware, but it could mean other data too.
The number of comments on a page may be used by Google as a quality signal, i.e. lots of comments means good user interaction, so is probably a good quality page.
This is sometimes referred to as dwell time. It is the amount of time that a person spends on your page and website after clicking on a link in a search result. If people spend a lot of time, you may get a boost.
On some search queries, the freshness of the results is important. Google identifies these keywords and gives new pages and updated content priority. This is known as the query deserves freshness (QDF) algorithm.
Some keywords have multiple meanings. In these cases Google will deliberately make the search result diverse. This is known as the query deserves diversity algorithm.
This only works when a user is logged into Google. When they are their search history is a ranking factor. Sites they visit frequently get a boost.
Google uses your search history to make results more relevant. For example, if you search for a number of different phone brands, and then you search for Apple, it is more likely to show you results about Apple phones than Golden Delicious apples.
A user is more likely to see websites in search results pages that are hosted on a local server and have a relevant country TLD.
When Safe Search is on, results that contain adult content or swearing are removed.
Google gives a boost to both authors and websites that you have added to your Circles in Google Plus.
Google penalizes websites that have valid DMCA complaints against them.
A previous algorithm update, commonly referred to as the Bigfoot Update, increased the number of root domains that appear in individual search results pages to increase the diversity of results.
Google is known to display differing search results for keywords that have a shopping intent, otherwise known as transactional keywords.
On a local search, Google will usually put results from Google My Business (Google Local) above other results.
For some keywords, Google displays a number of Google News results.
Google gives big brands preference over smaller websites for some short-tail keywords. This is probably because big brands have built up more trust over time. This change was implemented as part of the Vince algorithm update.
For some keywords, Google displays Google Shopping results on the page in preference to organic listings.
If a keyword is regularly used in Google's Image Search, it might display some of those results in the main search pages in preference to organic listings.
Google has a number of quirky results for a small list of certain keywords. For example, searching for the keyword "do a barrel roll" the page will do a barrel roll. Searching for "Atari Breakout" using Image search, turns the page into a version of the classic game - which you can actually play!
Searching for keywords that are obviously related to a particular domain or brand will show multiple results from the same website.
Many experts believe the number of tweets that a page gets is a ranking factor.
Tweets from accounts that have authority (usually because they are long-standing and/or have lots of followers) are probably worth more than accounts with less authority.
Google doesn't have access to all the information on Facebook accounts, so this is probably a small ranking factor. It is thought by many that the number of likes a page has does count though.
A share is regarded as a greater vote of trust in a page than a Facebook like, so is probably worth more as a Google ranking factor.
Likes and shares from Facebook pages that have authority (have been around for a long time and are popular) are worth more than pages that are not popular.
It is thought that Google takes an interest in Pinterest because of its popularity, and because there is a lot of data that it can access.
Many believe Google uses shares and other social signals from sites like Digg, Reddit and Stumbleupon.
Back in 2012 Matt Cutts said +1s on Google+ have no impact on search rankings. If Google is using social signals from other platforms, however, it is likely to be using signals from its own too.
This follows on from the previous point. If you believe that it uses signals from its own social platform, it probably gives accounts with greater authority more influence.
The Google+ authorship initiative did not last long, but most people believe that Google still uses something similar as a ranking factor, albeit less publically. This means boosts for content from people that it knows and that have influence.
Relevancy is important in on-page and link factors, so it is probably important with social signals too. That means signals from accounts that have relevance to your industry or niche will be worth more than unrelated accounts.
Many believe site-wide socials signals could boost all pages from that website in search.
Anchor text that includes the brand name of the site it is linking to is a significant ranking factor.
When a person does a search with a brand-related keyword, they will probably be shown search results from that brand.
Facebook boosts brands for some results, so it has to understand if a website is a legitimate brand. One of the ways it probably does this is checking if the website has a Facebook page, and if that page has likes.
The point mentioned above about Facebook applies to Twitter accounts and followers as well.
The two points above also apply to LinkedIn. Most legitimate businesses have a Facebook page, Twitter account, and LinkedIn company page.
Some SEO experts believe that employee LinkedIn profiles could be a ranking factor. In particular, it helps when an employee lists your company as their employer.
Not all social media accounts will be treated the same by Google. It is not all about likes and followers either. For example, an account with lots of likes and lots of interaction will be valued more than a page with lots of likes but very few posts and no interaction.
Brands get mentioned in the news. Google probably uses this to identify brands and judge their authority.
These are mentions on pages without a link. This is common for many brands, particularly large brands, so Google probably uses it as a factor.
The number of RSS subscribers that a brand has is probably a ranking factor. It indicates popularity and shows it is a real brand.
Legitimate businesses have offices, so one of the ways Google probably identifies brands is by looking at their address details.
This one comes from Moz. They think that Google might use tax when determining if a website is a legitimate business, i.e. if the business pays tax, the website is more likely to be real.
Panda devalued websites with low quality content. Content farms, for example, now appear much lower.
"Bad neighborhoods" is a broad term that covers everything from link farms to dodgy payday loan and pharmacy websites. If you link to these sorts of websites you might damage your rankings.
Cloaking and other types of redirecting trickery are likely to get you severely penalized and possibly thrown out of the index. Cloaking is giving a user different content to the content that you tell Google is on the page.
Google regards the presence of popup ads and other types of distracting ads as an indicator of a low-quality website.
Examples of this include keyword stuffing, or putting loads of keywords in the header tags. This might have worked in the past but it has been a useless strategy for years now.
This works the same as the previous point. The Penguin update beefed up Google's ability to identify over-optimized pages.
Google believes that pages that do not have much content above the fold, or are stuffed with ads above the fold, offer a poor user experience. The Page Layout Algorithm resulted in pages like this getting penalized.
Making an affiliate link more user-friendly is normal, but trying to hide it completely might damage your rankings. This is particularly bad if cloaking tactics are employed.
Many people believe that websites that use affiliate links as a major revenue generating strategy may be more closely monitored or treated differently than other websites.
Google lists autogenerated content in its Quality Guidelines. This is a big indicator that such content should not be used.
PageRank sculpting is the practice of tweaking your site, particularly links, in an attempt to control the flow of PageRank. An example is making all your links nofollow. Google doesn't like it though, and it could harm your rankings.
Some spam penalties from Google apply to IP addresses, not just individual websites. That means websites on a shared IP could be impacted by a penalty issued to another site on the server.
Stuffing keywords into your meta tags will probably hurt your rankings.
A website that starts getting a load of links quickly, particularly if those links have an unnatural profile, could be penalized.
Google's Penguin update decreased rankings for websites that used black-hat SEO strategies to increase the number of links.
Even sites that escaped the Penguin update, but have a high percentage of links from low quality sources, can be penalized. This means lots of links from things like blog comments.
One of the things the Penguin update put under closer scrutiny was the relevancy of the domains linking to your website. If lots of those domains are regarded as being unrelated to your niche or industry, you may be hit with a penalty.
An unnatural links warning from Google usually means the link profile of your site should be fixed, or you might see a drop in rankings.
Lots of links from the same Class C IP indicates to Google the links may be unnatural, so might result in a penalty.
Poison anchor text usually refers to anchor text containing pharmacy-related keywords. These are often used by spammers, or by hackers planting malicious code on a site. If links are pointing to your site using poison anchor text, you could suffer a drop in rankings.
Not everything Google does is algorithm-based. It has been known to dish out manual penalties as well.
Since 2007, Google has issued PageRank penalties to websites that sell links.
New websites are often put into the Google Sandbox. This is like putting a website on probation, and means the site appears much lower on search results than its content on links warrant. It is in place to put off spam sites starting up, ranking well, riding the wave until they get penalized, and then starting over again.
The Google Dance is where Google shakes up the rankings. The effect can be temporary, and it is often used to identify spam sites.
The Disavow Tools allows website owners to tell Google not to count certain links to their site. It is often used in attempts to remove a penalty.
If this is successful, a previously applied penalty can be lifted
Temporary link schemes are a blackhat SEO technique. Google penalizes sites it believes use the method.