The way Google generates the descriptions (snippets) that appear under a page in the search results is completely automated. This process uses both the content on a page as well as references to it that appear on other sites.
While some people like to generate snippets with Open Directory Project, or ODP, others request not to use ODP to generate snippets. Google came out with a support system which merely calls for adding a meta tag to your pages.
You can use the following code to direct all search engines that support the meta tag not to use ODP information for the page's description-
<META NAME="ROBOTS" CONTENT="NOODP">
Remember, not all search engines may support this meta tag. To direct Google specifically from using this information to describe a page, you can use the following:
<META NAME="GOOGLEBOT" CONTENT="NOODP">
As you add meta tag to your pages, it might take a considerable time for changes to appear to your snippets. Because there is the question of recrawling of pages. For more information, visit the webmaster help center.More Control Over Page Snippets,