Meta tags are found at the top of a page's source code. They are used to specify certain things that might not be found in the page content. They also allow webmasters to put up certain "flags" that search engine crawlers can react to. There are many Meta tags available for use, and many of them can help with SEO to a great extent and for a variety of purposes. However, Meta tags are no longer used in the way they originally were - as a place to stuff keywords to drive your site up in rankings. Some webmasters out there are still doing this, but they are decidedly behind the times and unaware of the impending, or already cast-down, penalties.