Definition of committed
Literally "committed". A "committed" poker situation is one where a player has no choice but to go all in considering what he has already invested in the pot, the size of the pot and his equity in the hand. "I'm committed, I have no choice but to call. When you are committed to a pot, it doesn't mean you think you will win the hand often, but we know that in the long run, it is the game to be played.
An example of a hand where we are committed
You are in a tournament with A2 in spades on the button. You open your hand preflop after the players before you folded. Both blinds call your raise. The flop is 4-5-8 with two spades. The small blind bets the flop, the big blind calls, you raise to 12 big blinds (all players had 50 big blinds before the hand started), the small blind pushes all in, the big blind calls and the call is yours. Here, you only have an ace draw. It is possible that one or both players have a much stronger hand than you, but given all the money in the pot and your equity, you are committed to the pot and must call all in.