The Meta description is the two line summary displayed in SERP. Generally, the description is 155 chars, but more characters the automatically truncated by Google. The keywords in meta description are used in ranking purpose [Google updated this in Sep 2009 that it do not use meta description for ranking] but proper meta description will improve the Click through rate (CTR) for the page.
Meta Description Code:
<meta name=”description” content=”Write the brief summary of the page and explain precisely about the page” />