I'll use my same answer from this question:
A few years back, meta tags were important to search engine optimization. However, they've been abused and are generally ignored by almost all search engines (including Google, Yahoo and Live search. Excuse me: Bing).
The most important tags for SEO that you can include in your (X)HTML are the <title>
and <meta name="description"...>
tags.
<title>
should generally be what you'd want the search engine to name your page in it's listing.
<meta name="description"...>
can sometimes give the search engine a basic idea of how to describe your page when indexing it.
However, using these two tags will not necessarily make a difference in increasing your site's visibility on a search engines listings. For more information on that aspect, Google has a nice section on SEO on their site.