An algorithm is the complex calculation that search engines use to determine what web pages to show a searcher when he or she searches for a particular keyword phrase. A search engine's job is to determine which web pages out on the world-wide web are the most relevant, useful, and important for each particular keyword phrase a searcher may enter. An algorithm is the mechanism search engines use to make this determination.

You can think of an algorithm as a really long, ugly mathematical equation. Algorithms consider many, many factors (of varying importance and weight) in determining how web pages rank relative to other web pages. All of these factors are considered in the algorithmic calculation.

Companies (such as Google) that operate search engines are constantly changing and updating their algorithms in an effort to improve the quality of the results their search engine provides. Google and the other search engines do not disclose exactly how their algorithms work, but they do give hints as to what types of factors are considered. These factors should of course be considered by website owners as they attempt to search engine optimize their web pages so they are treated favorably by search engines. The factors include:

• The web page's meta tags and textual content
• The age of the domain name
• The PageRank (PR) (i.e. importance or authority) of the web page and of the root domain name that the web page is on
• The words included in the URL of the web page
• The number and quality of the backlinks pointing to the web page
• And many other factors