An elevator pitch is an explanation of what you do in 30 seconds or less. If you were in an elevator with a prospect could you explain what you do before you get to your floor?
An elevator pitch is important because it crystallizes what you are about. I have talked to people for 2 hours and they couldn't explain what they did. Considering you have a brief window to get your message across you should be prepared with your elevator pitch at a moment's notice.
What is your elevator pitch?