Description meta tag
The description meta tag is not necessarily important from an SEO point of view. It does hold a lot of importance though because it is shown in the search results, just under the title. That gives you an opportunity to write a message that gets the users to click on your link.
Same as the title meta tag, if the rescription exceeds 165 characters, it will be truncated by the search engines and the message will not be shown entirely. This will in turn lower the click rate.