When search results are displayed on Google, the descriptive text below the page title is called the snippet. See example below:

Matt Cutts from Google recently videotaped a bunch of impromptu tech-oriented videos (I think he stole the idea from me <g>), one of which was how Google comes up with the snippet. Hint: it's not always your meta description tag, and sometimes it's even your DMOZ description! :/

You can view the video, or view notes courtesy of Eric Enge. I personally prefer to skim notes in 2 minutes instead of watching a 10 minute video, but that's just me...