Meta Description: A meta description is a type of meta element, which is a tag used in HTML or XHTML to express meta data about a specific web page. Specifically, a meta description refers to a sentence or so of content which describes the web page's content. Most search engines require the description to be shorter than 155 characters of plain text. Search engine users will typically see meta description tags in search results, below the page title. Most major search engines, including Yahoo! and Bing, use meta descriptions. However, Google only offers meta descriptions when information about the page is requested.
By including meta descriptions, web page authors are able to give a more effective and meaningful report on their page's content than what a search engine might automatically generate. Meta descriptions can have a significant effect on click-through rates, as search engine users can gather a better sense of whether or not a web page applies to their search by reading about what the page's content might include. Some industry commentators have suggested adding keywords to further improve this ability.