Meta description and meta title are both an HTML tag attributes in page headers section that provides a brief summary of a web page content. Search engines like Google or Yahoo display them in search results. First title that is linked to a web page and right below meta description. While both, meta description or meta title, might be any length size the preview space for a long time limited their sized to 55-56 for titles and 160 for description. Recently Google made an updated and increased visible length for both tags. Now search results show 76-77 characters for title and sometime up to 220 characters for meta description.
Alexa recommends limiting web page title to 60 characters and keep description below 320 characters.
Remember, that title tag is the most important meta tag for search engines, description is the second. Try to use your most important keywords in title and then repeating them in description.