Back-Links: also known as incoming links, inbound links, inlinks, and inward links, are incoming links to a website or web page. This is NOT the same as a reciprocal link.
In basic link terminology, a backlink is any link received by a web node (web page, directory, website, or top level domain) from another. Inbound links were originally important (before the emergence of search engines) as a primary means of web navigation; today, their significance lies in search engine optimization (SEO). The number of backlinks is one indication of the popularity or importance of that website or page (for example, this is one of the factors considered to determine the PageRank of a webpage). 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. This is also called “link juice”. 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 have content geared toward the keyword 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.