Guard crush values are assigned to characters and moves in games that implement a guard crush system. Much like dizzy values, they are not usually displayed (but some games do, displaying the guard crush potential on a dedicated meter known as the guard gauge).
As a character blocks moves, they accumulate guard crush values, and once they reach their limit, they will be guard crushed. Guard crush values almost always recover slowly over the passage of time.
The usual difference between the values for guard crush and dizzy (besides, of course, their effects) tends to boil down to two factors: the guard crush capacity tends to be the same for every character in a game, and that capacity usually does not change even if a guard crush is performed. Thus, in most games, anything that will guarantee a guard crush when blocked will guarantee it regardless of how many times someone has been guard crushed.