What is the description attribute?

Unlike the keyword attribute, the description attribute is supported by most major search engines, like Yahoo and Live Search, while Google will fall back on this tag when information about the page itself is requested (e.g. using the related: query). The description attribute provides a concise explanation of a Web page's content. This allows the webpage authors to give a more meaningful description for listings than might be displayed if the search engine was unable to automatically create its own description based on the page content. The description is often, but not always, displayed on search engine results pages, so it can impact click-through rates.

Industry commentators have suggested that major search engines also consider keywords located in the description attribute when ranking pages. W3C doesn't specify the size of this description meta tag, but almost all search engines recommend it to be shorter than 200 characters of plain text.