There are several factors that determine the value of a backlink. Backlinks from authoritative sites on a given topic are highly valuable. If both sites and pages have content geared toward the topic, the backlink is considered relevant and believed to have strong influence on the search engine rankings of the web page granted the backlink. A backlink represents a favorable 'editorial vote' for the receiving webpage from another granting webpage. Another important factor is the anchor text of the backlink. Anchor text is the descriptive labeling of the hyperlink as it appears on a web page. Search engine bots (i.e., spiders, crawlers, etc.) examine the anchor text to evaluate how relevant it is to the content on a webpage. Anchor text and webpage content congruency are highly weighted in search engine results page (SERP) rankings of a webpage with respect to any given keyword query by a search engine user.
Website owners recognized the value of a high ranking and visibility in search engine results, creating an opportunity for both white hat and black hat SEO practitioners. According to industry analyst Danny Sullivan, the phrase "search engine optimization" probably came into use in 1997. Sullivan credits Bruce Clay as one of the first people to popularize the term. On May 2, 2007, Jason Gambert attempted to trademark the term SEO by convincing the Trademark Office in Arizona that SEO is a "process" involving manipulation of keywords and not a "marketing service."
Search engines are smart, but they still need help. The major engines are always working to improve their technology to crawl the web more deeply and return better results to users. However, there is a limit to how search engines can operate. Whereas the right SEO can net you thousands of visitors and increased attention, the wrong moves can hide or bury your site deep in the search results where visibility is minimal.
There is much discussion in these last few months about reciprocal linking. In the last Google update, reciprocal links were one of the targets of the search engine's latest filter. Many webmasters had agreed upon reciprocal link exchanges, in order to boost their site's rankings with the sheer number of inbound links. In a link exchange, one webmaster places a link on his website that points to another webmasters website, and vice versa. Many of these links were simply not relevant, and were just discounted. So while the irrelevant inbound link was ignored, the outbound links still got counted, diluting the relevancy score of many websites. This caused a great many websites to drop off the Google map.
A backlink is a reference comparable to a citation. 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. 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. This weighting of backlinks is analogous to citation analysis of books, scholarly papers, and academic journals. 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.