The search algorithm is a computer program that visits almost all the sites on the Internet, ranks the contents of all these sites for all sorts of keywords and when a user request returns the page most relevant keywords of this query based on your ranking pages of all sites for those keywords. At the last stage before entering the received search results, the ranking of the pages is filtered may, in accordance with certain principles. So, essentially, search algorithms had to be called ranking algorithms, but historically that is called search.
The main goal of search algorithms – results of high quality content on this keyword. But the intrigue lies in the fact that despite all the advances of artificial intelligence in General and machine learning in particular, the meaning of the search algorithms still do not understand and, consequently, the quality of written fully independently. Therefore, along with the formal definition of quality of content and formal indicators of structure, in particular based on the links to this content from other sites as a kind of vote in support of this content. At the moment, to forge formal features of structure, maturity of the text more complex than "to forge" links-voices from external sites, so the latter often become objects of manipulation. Because of this, the developers of search algorithms used, whenever possible, the least manipulated links which exist at this stage of technological development.