Meta tags <meta> are a component of the invisible part of your HTML page — all that stuff between the <head> </head> tags. So far, you probably haven’t seen much beyond the <title> tag in there, but now I’ll show you a few more. None of these tags will actually change how your page looks, they are purely for search engine's use and to provide some additional information about your pages.
Meta tags were the original way to tell search engines what your page was about. You’d add a description and a number of keywords into your meta tags, and a search engine would come along to “index” your page, read these words, and file your site under them.
How to Use a Meta Tag
Meta tags are included in the <HEAD> of an HTML document. If you are using meta tags to improve your standing in search engines, then you should focus on your description and keywords.
The description tag
Use the description tag to describe what your page is about. Engines that use it will supply the content of this tag when displaying a list of links. For example, if you do a search on About.com, you will see the description listed on the search results page.
The keywords tag
Keywords help search engines to categorize your site, and to allow people to find your pages more quickly. However, most search engines have limits as to how many meta keywords are viewed. It is a good idea to review your keywords and make sure that they are as concise and specific as possible.