The keywords tag, invisible part of your webpage) is used by a meta capable search engines to help aid in indexing your web site. Search engines use this information to determine under what relevant queries your web site will come up under. Since most searches are now done by combining word phrases,75% by recent studies.
Search engines may use metadata when indexing and classify website content. Standard meta-information includes:
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<meta name="description" content="Description of the page content" />
<meta name="keywords" content="Synonyms and phrases that classify page content" />
Keyword search is a search for documents containing one or more words specified by a user in a search engine text box.
A meta tag that allows the author to emphasize the importance of strategic words and phrases used within a Web page. Some search engines respond to this information, others ignore it. Don't use quotes around keywords or key phrases.
Meta Search Engine: A server that passes queries on to many search engines and directories, then summarizes the results. Ask Jeeves, Dogpile, Metacrawler, Metafind and Metasearch are meta search engines.
Meta tags: Information placed in the HTML header of a Web page, providing information that is not visible to browsers. The most common meta tags relevant to search engines are keyword and description tags.