Stands for search engine optimization, the process of increasing the amount of visitors to a Web site by high rank 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 site will be visited by a user. In general Internet users 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.

Search engines display different kinds of listings on a results page, including paid advertising in the form of sponsored links listings, as well as unpaid organic search results and keywords specific listings, such as news stories, definitions, map locations, and images. SEO is concerned with improving the number and position of a site's listings in the organic search results not in paid links.

Search engine optimization is available as a stand-alone service. 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.

SEO principles
1- Text: Use content that includes words and phrases your company's target audience is likely to type into search queries. If you're selling Books, that term should be everywhere -- in page headings, navigation buttons, photo captions and the like.
2- Links: A site's navigation scheme should be accessible, coherent and consistent so that spiders and humans can easily traverse it.It should have title in link tag.
3-Popularity: A good site will prompt others to link to it. External links from reputable sites will enhance your Web site's ranking in search engines.