The meta description tag and the meta keywords tag are not seen by users. Instead, these tags main purpose is providing meta document data to user agents, such as search engines. In addition to the well-known meta description and meta keywords tags, there are other useful meta tags, including the meta http-equiv tag, meta refresh tag, the meta robots tag, the meta copyright tag, and the meta author tag, etc. These tags are used to give web browsers and search engine spiders directions or data on various information.
If you really feel like getting technical, take a look at this document . This is put out by the governing body on web design, and is an official W3C recommendation.