What Backlinks Are and the Importance of Backlinks in Search Engine Optimization

The Definition of Backlinks as explained in Encyclopedia:

Backlinks (or back-links (UK)) are incoming links to a website or web page. In the search engine optimization (SEO) world, the number of Backlinks is one indication of the popularity or importance of that website or page (though other measures, such as PageRank, are likely to be more important). Outside of SEO, the Backlinks of a webpage may be of significant personal, cultural or semantic interest: they indicate who is paying attention to that page.

In basic link terminology, a backlink is any link received by a web node (web page, directory, website, or top level domain) from another web node (Björneborn and Ingwersen, 2004). Backlinks are also known as incoming links, inbound links, inlinks, and inward links.

How Backlinks Affect Your Page Ranking

Search engines often use the number of Backlinks that a website has as one of the most important factors for determining that website's search engine ranking. Websites often employ various techniques (called search engine optimization) to increase the number of Backlinks pointing to their website. Some methods are free for use by everyone whereas some methods like linkbaiting requires quite a bit of planning and marketing to work.

There are several factors that determine the value of a back link. Backlinks from authoritative sites on a given topic are highly valuable. If both sites have content geared toward the keyword topic, the back link is considered relevant and believed to be have strong influence on the search engine rankings of the webpage granted the backlink. A backlink represents a favorable 'editorial vote' for the receiving webpage from another granting webpage. Another important factor is the anchor text of the backlink. Anchor text is the descriptive labeling of the hyperlink as it appears on a webpage. Search engine bots (i.e., spiders, crawlers, etc.) examine the anchor text to evaluate how relevant it is to the content on a webpage. Anchor text and webpage content congruency are highly weighted in search engine results page (SERP) rankings of your webpage with respect to any given keyword query by a search engine user.

How to you know what your Backlinks Are

Most commercial search engines provide a mechanism to determine the number of Backlinks they have recorded to a particular web page. For example, Google can be searched using link:wikipedia.org (or link:en.wikipedia.org) to find the number of pages on the Web pointing to http://wikipedia.org/.

Yahoo!’s Site Explorer is a method of obtaining the number of Backlinks on a site.

Keeping Track of Backlinks

When HTML was designed, there was no explicit mechanism in the design to keep track of Backlinks in software, as this carried additional logistical and network overhead.

Some website software internally keeps track of Backlinks. Examples of this include most wiki and CMS software.

Other mechanisms have been developed to track Backlinks between disparate webpages controlled by organizations that aren't associated with each other. The most notable example of this is TrackBacks between blogs.

Understanding Page Ranking is Key

See an excerpt from Whibbly

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The first thing that you need to keep in mind is that there are two PageRanks. The nominal one, which is the one that shows on your Google toolbar, and which gets updated once every three months or so, and the real one, which gets updated constantly and is used inside Googles search algorithm.

The first one is used just to provide an indication for webmasters, while the second will have a direct influence on your search rankings.

Now back to your question, does PageRank only depend on the number of inbound links, also called Backlinks?

The answer is no.

The number of Backlinks certainly plays a role, but Google also evaluates carefully the quality and relevancy of those links.

By quality I mean the overall trust that the site that linked to you has. A link from the Stanford university would have more quality than one from your sister’s blog. Another way to call quality is authority.

By relevancy I mean the proximity of the content on the website that is linking to you, to your own content. If you have a blog about cats, a link from your sister’s blog that talks exclusively about cats too would be more relevant than a link from the Quantum Physics department of the Stanford university...

Let’s consider a example to understand this better. Suppose you just launched two blogs, A and B. Both blogs talk about technology. On the first blog you decide to purchase 30 Backlinks from very small and unrelated sites (most of which don’t even have PageRank to begin with). On the second blog, on the other hand, you just publish one quality article, and that article gets linked from the homepage of TechCrunch.

If you wait three months and don’t change anything else on the blogs, it is very likely that the the first one would end up with no PageRank at all, while the second one would probably end up with a PR1.