tedster - 7:03 am on Sep 6, 2012 (gmt 0)
Literally "meta" means a concept that is an abstraction from another concept. So in psychology, meta-memory is remembering if you actually remember something. In an html document meta data is data ABOUT the document's data, so a "meta tag" is a short bit of information about the the html document. That's why any meta tag should always be in the <head> area.
There are many meta tags, and only few have influence on either the major web search engines or on browsers. Other meta tags have custom purposes that may be used internally by the business, or some specific business. Even Google offers a custom site verification meta tag.