A backlink is a link from some website (the referrer) to that web resource (the referent). A backlink is a reference comparable to a citation. The quantity and sources of backlinks for a web page are among the factors that Google's PageRank algorithm evaluates in order to estimate how important the page is. When adding backlinks make sure the website you are adding the backlink to is compatible to your website and has a good reputation. Bad site can afffect your ranking. So remember not all backlinks are created equaly. You need quality and not quantity.