As far as high ranking is considered to be very important part of SEO same ways an attractive description in the displayed search results is very important for our website link to be clicked by the web surfers.
You must be wondering on this how do these top search engines take the description to be shown with the search results, below are the process followed by the top two Search engines (GOOGLE and YAHOO) to grab the description for the display of search result.
- How Google creates descriptions and snippets
Google seems to use the description from the Meta description tag if you search for a page by its URL, or if the searched keywords do not appear within the found page. If that web page doesn't have a Meta description tag then Google might also use the description that is used in the DMOZ directory.
- How Yahoo creates descriptions and snippets
Yahoo seems to use only the first part of the Meta description, but If a web page doesn't have a Meta description, Yahoo will use the description of the web page from Yahoo's directory (if the page is listed there). If the web page has no Meta description and is not listed in the Yahoo directory, then Yahoo will display sentences from the found web page that contain the searched keywords.
If you don't want to use the description that is used in the Yahoo directory and on DMOZ.org you should use the corresponding tags that prevent search engines from using these descriptions.