A backlink for a given web resource is an association from some other website (the referrer) to that web resource (the referent). A web resource may be (for example) a webpage, site page, or web list. A backlink is a reference identical to a reference. The sum, quality, and essentialness of backlinks for a site page are among the components that web crawlers like Google survey to assess how critical the page is. PageRank calculates the score for each page subject to how all the pages are related among themselves, and is one of the variables that Google Search uses to choose how high a page should go in list things. This weighting of backlinks is like reference assessment of books, savvy papers, and insightful journals. A Topical PageRank has been examined and executed likewise, which gives more weight to backlinks beginning from the page of an equal subject as a goal page.