What is a Backlink? Well, its very simple actually, a Backlink is just a DoFollow link pointing to a website. I’t’s useful to have a collection of Backlinks pointing to your website because they are used by most major search engines such as Google, Bing, and Yahoo! to determine the trust level of your website.
The basic concept is that the more links you have going to your site the better quality the content on the site is and thus it should be ranked higher in search engines. Backlinks also transfer page rank from site to site based on a variety of factors. The major factor is the PageRank of the site who is linking to another site. PageRank is the quantifiable way for search engines to express how much they trust your website ranging from PR1 to PR 9.
If you are linked to by a site with very low PageRank (PR) that is considered a Low-Quality Backlink because it’s not coming from a reliable source and is thought of by web spiders as a spam backlink. There are also High-Quality Backlinks which give search engines a much better impression of your site because they usually come from PR6 to PR9 Websites that are already trusted by search engines. These Backlinks are also weighted more heavily than Low-Quality ones because they are coming from a source that is known not to spam links to low-quality sites.
There are a few exceptions to the Low and High-quality backlink rules though. The major one is Social Networking sites like Facebook that have high Pageranks but only give low-quality backlinks. The reasoning behind this is pretty simple, search engines give backlinks from these sites less value because they are usually mass posted, and can easily be posted by the website owner. This is not a bad thing though as if Backlinks from Social Media sites were worth PR9 status then a link in a Tweet would be the same as being mentioned in a post on Forbes.com or NYTimes.com.
The last factor that search engines look at is the mixture of High and Low-quality backlinks. What this means is if a site only has Low-Quality backlinks then chances are that site has been spamming small blogs and social media site. But if a site has a Mix of High and Low-Quality backlinks then it tells Google that your site is linked to being trustworthy sites and shared allot by its users and thus it must have super great content.