SEO is short for Search Engine Optimization, the process of increasing the amount of visitors to a Web site by ranking high in the search results of a search engine. The higher a Web site ranks in the results of a search, the greater the chance that that site will be visited by a user. It is common practice for Internet users to not click through pages and pages of search results, so where a site ranks in a search is essential for directing more traffic toward the site.

SEO helps to ensure that a site is accessible to a search engine and improves the chances that the site will be found by the search engine.

Search engine optimization (SEO) as a subset of search engine marketing seeks to improve the number and quality of visitors to a web site from “natural” (“organic” or “algorithmic”) search results. The quality of visitor traffic can be measured by how often a visitor using a specific keyword leads to a desired conversion action, such as making a purchase or requesting further information. In effect, SEO is marketing by appealing first to machine algorithms to increase search engine relevance and secondly to human visitors. The term SEO can also refer to “search engine optimizers”, an industry of consultants who carry out optimization projects on behalf of clients.

Search engine optimization is available as a stand-alone service or as a part of a larger marketing campaign. Because SEO often requires making changes to the source code of a site, it is often most effective when incorporated into the initial development and design of a site, leading to the use of the term “Search Engine Friendly” to describe designs, menus, Content management systems and shopping carts that can be optimized easily and effectively.

A range of strategies and techniques are employed in SEO, including changes to a site’s code (referred to as “on page factors”) and getting links from other sites (referred to as “off page factors”). These techniques include two broad categories: techniques that search engines recommend as part of good design, and those techniques that search engines do not approve of and attempt to minimize the effect of, referred to as spamdexing. Some industry commentators classify these methods, and the practitioners who utilize them, as either “white hat SEO”, or “black hat SEO”.Other SEOs reject the black and white hat dichotomy as an over-simplification.