What is a "parlay," and why make it?

[emp1346]

So I understand sports betting, lines, and all that fun stuff. I guess I learn something new everyday, because one guy I know said he only bets "parlays." I've never heard of this.

He tried to explain it, but after listening to him I'm surprised he even knows what he's talking about. He started talking about pulling from the parlay pool only when he needed it, and some other stuff that didn't make sense.

Can someone explain what a parlay is, and why you would make it?