Meta tags are hidden descriptions of a Web page. They describe the site's content so that search engines can more easily find what they are looking for. Meta tags are even more important for sites that contain frames or numerous graphics. They are used as part of your HTML code, and by some search engines to index your page. Rather than letting the search engine take the first few words or paragraphs to use as your keywords, meta tags allow you to tell the engines what to use.
Excerpted from 101 Internet Marketing Tips For Your Business