A backlink is a link from some other website (the referrer) to that web resource (the referent).[1] A web resource may be (for example) a website, web page, or web directory.[1]
A backlink is a reference comparable to a citation.[2] The quantity, quality, and relevance of backlinks for a web page are among the factors that search engines like Google evaluate in order to estimate how important the page is.[3][4] PageRank calculates the score for each web page based on how all the web pages are connected among themselves, and is one of the variables that Google Search uses to determine how high a web page should go in search results.[5] This weighting of backlinks is analogous to citation analysis of books, scholarly papers, and academic journals.[1][4] A Topical PageRank has been researched and implemented as well, which gives more weight to backlinks coming from the page of a same topic as a target page.[6]
Some other words for backlink are incoming link, inbound link, inlink, inward link, and citation.[1]
Backlinks are offered in Wikis, but usually only within the bounds of the Wiki itself and enabled by the database backend.[7] MediaWiki specifically offers the "What links here" tool, some older Wikis, especially the first WikiWikiWeb, had the backlink functionality exposed in the page title.[8]
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, popularity and importance.[9] Google's description of its PageRank system (January 1998), for instance, noted that "Google interprets a link from page A to page B as a vote, by page A, for page B."[10] Knowledge of this form of search engine rankings has fueled a portion of the search engine optimization (SEO) industry commonly termed linkspam, where a company attempts to place as many inbound links as possible to their site regardless of the context of the originating site.[11] In January 2017, Google launched Penguin 4 update which devalued such link spam practices.[11]
The significance of search engine rankings is high, and it is regarded as a crucial parameter in online business and the conversion rate of visitors to any website, particularly when it comes to online shopping.[12] Blog commenting, guest blogging, article submission, press release distribution, social media engagements, and forum posting can be used to increase backlinks.