The Description Meta tag defines the site information most search engines will display when they list the site. (The top search engines, Google, Yahoo!, MSN, and Ask.com! often will display a snippet of body text that includes the keyword(s), instead.) The site description should provide a concise and enticing introduction to the site's contents. The description should include as many site keywords as possible, but the main purpose of the "description" Meta is to convince the Internet user to take a look inside. If applicable, each page of a Web site should feature its own, unique "description" Meta tag.
Limitations vary, but "description" Meta tag content should generally not exceed 250 characters, including spaces.
See below for example:
<head>
<title>Hogwarts Express — A Harry Potter Fan Site</title>
<meta http-equiv="content-style-type" content="text/css">
<meta http-equiv="content-type" content="text/html">
<meta name="rating" content="general">
<meta name="distribution" content="global">
<meta name="description" content="The ultimate Harry Potter site. Features a wealth of Harry Potter resources, including news, message boards, reviews, multimedia and merchandise.">
<meta name="keywords" content="Harry Potter, Potter, Potter fans, Potter news, Potter Merchandise, Potter T-shirt, Potter reviews, Potter images, Potter downloads, Hogwarts, Hogwarts Express, JK Rowling, Rowling, muggle, wizards, children's books, lightning bolt.">
</head>