What is Pot-Committed?

Answer 1

In simple terms it means where you are in a position (risk reward) where the only sensible thing is call or bet, NOT fold, even though you think the likely outcome is that you will lose. This is very closely related to calculating your pot odds, the amount you can win considering what the chance is of your winning.

Answer 2

Most often used in No-Limit games, being pot-committed means you are unable to fold due to the size of the pot, and the size of the bet you must call to win it.