What is fantasy football?

OK, sometimes I feel like I'm in a Twilight Zones episode. Today at work some of the younger guys were talking about Jason Taylor at the watercooler, so I made my way over. Then they start talking about drafting him - uh, what? Guys, Jason Taylor is a 12-year vet! I said this and they just started laughing at me. "It's fantasy football, Pete" they said. Fantasy football? Every football fantasy I ever had came true when Jason "Taylor Made" Taylor came to the 'Skins. They tried to explain it to me but they might as well have been speaking Chinese. I just don't get it. What is fantasy football and what's the point?