Pot committed means the right thing to do is to continue putting money in the pot. You are pot committed when your pot odds are sufficient to call - it's as simple as that. You may also encounter this term being used to indicate your stack is so small that there's no point in folding - regardless of the pot odds.

Odds Committed

You are pot committed when a call is warranted strictly through pot odds. Interpretation of the situation or the players is some distant consideration. For this calculation one considers only their guaranteed outs -- those cards which give them the nut hand, or one quite close to it. The outs are then used to calculate the expected value. If the expected value is greater than the required pot contribution, a call is warranted.

This is a strictly mathematical calculation. There is no reason to ever fold in such a situation: calling with an expected value greater than the required call is a long-term winning proposition.

A player is only committed to the pot when their pot odds are greater than their losing odds. Simply having sufficiently high pot odds is not a legitimate commitment to the pot. While 20:1 pot odds sound great, it is still incorrect to call if the losing odds are 25:1 or worse. High pot odds are no excuse to call under the banner of being pot committed.

The phrase also tends to indicate a true commitment, which would imply every player in the same situation would arrive at the same conclusion: no choice but to call. Considering the actions of other players, or counting possible and potential outs, starts to muddy the clarity. A decision factor means only one thing: a reasonable alternate choice. Since there are now at least two choices, the player cannot be said to be pot committed.

Insufficiently Committed

Many players also consider that a severely crippled stack is somehow also pot committed. That is, if the stack is incapable of sufficiently playing another round then it should just be moved all in and take a chance at the current pot.

In a ring game this is a losing strategy. Long term it will simply net more loss than gain. Yet frustration, tilt, or the desire to gamble cause many a player to do exactly this move. Psychologically a player may simply not value the amount at this point, that is they consider the call amount to be effectively zero thus giving them infinite pot odds. Or simply the thrill of winning the long-shot would be so much that they simply can't avoid trying it. Long-term they'll still lose, but they'll only ever remember the one time they won.

In a tournament the situation can be different. As no rebuy is possible, a severely crippled stack in most cases is the same as being knocked out of the tournament. Thus regardless of the odds being offered it may make sense to call with a tiny stack and hope for the long shot. This seems like a reasonable move for stack sizes less than the big blind as very few people would question it.

A stack size of greater than the big blind however is not automatically lost. It gives the player one more chance to play and earn enough chips to continue playing. Rather than the horrible 15:1 odds the current hand is offering, they could instead keep their money and pickup the first 8:1 or better odds dealt to them in a nine player game. As 40% of all pockets meet this criteria it is not an unreasonable proposition.