Meta Descriptions are divisive in terms of importance, some people love 'em, some can't be bothered. If you're undecided on meta descriptions and want to know if they even matter, read on and educate yo'self.
What is a Meta Description?
For some more indepth info on meta descriptions it's worth taking a look at this "vintage" post from the NLM vaults, cleverly titled "What is a meta description". While the blog is a bit old the info is still fairly up to date.
A Meta Description is the short excerpt underneath the blue Page Title <link to page title blog> and green URL in SERPs (search engine result pages). It's purpose is to provide a snippet of text so you can accuratley see what that particular page's content is and and help determine if it's the right result for you.
Are Meta Descriptions Important?
According to Jon, you don't need a Meta Description. Google is relatively adept at creating pretty useful meta descriptions on its own. Arguably you can leave your meta description blank. The real thing to avoid is having duplicate meta descriptions, this is seen as duplicate page content by search engines and is detrimental to your rankings.
Don't believe you don't need one? Matt Cutts will back us up!
Need to check for Duplicate Meta Descriptions? If only there was some Free Download...