Backlink:

A backlink is a link that one website gives to another. Backlinks are an important factor in search engine ranking.  If website A links to website B, it is a signal to Google that website A thinks website B is credible and a good source of information.  The more reputable website A is, the stronger the signal for Google.  If a website doesn’t want to give credit to a website it is linking to web masters might add the rel=”nofollow” attribute in the link’s code.  However, Google has recently changed how it is interpreting and added more options for the rel tag.