SEO is short for search engine optimization (or search engine optimizer). Search engine optimization is a methodology of strategies, techniques and tactics used to increase the amount of visitors to a website by obtaining a high-ranking placement in the search results page of a search engine (SERP) -- including Google, Bing, Yahoo and other search engines.
It is common practice for Internet search users to not click through pages and pages of search results, so where a site ranks in a search results page is essential for directing more traffic toward the site. The higher a website naturally ranks in organic results of a search, the greater the chance that that site will be visited by a user. 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. SEO is typically a set of "white hat" best practices that webmasters and Web content producers follow to help them achieve a better ranking in search engine results.