Pot committedA player is pot committed or committed if he has already invested so many chips in the pot that he can no longer fold if he is raised all-in.
For example, if a player has invested half of his stack in the pot and another player puts him all-in, then he will get pot odds of at least 3:1, meaning he must only win 25% of the time to break even. If there is other dead money in the pot, then his odds are even better.
If the player believes himself to be so far behind that he no longer has correct odds for a call, it is still correct to fold even if he has already invested a lot. It is wrong to call a raise just because you have already invested a lot of money in the pot, since money put into the pot no longer belongs to anybody.