My definition of a hero: someone who risks his or her life doing something that most people normally wouldn't do, and who isn't paid to do it. Here's an example:
[a href="vny!://www.msnbc.msn.com/id/12064900/"]vny!://www.msnbc.msn.com/id/12064900/[/a]
That guy is a hero. My definition completely bypasses police, firemen, astronauts, etc etc etc. Those people are paid to take risks, and a hero isn't.