It's a form of humiliation, usually this is something she's prompted to do by the master in the relationship, forced to say what she wants or else he'll punish her by denying it to her, essentially. Stating so explicitly and degradingly what she wants is humiliating, and masochist that she is, that gets her off.
That said, if you were looking for game that have it on here, as a tag, humiliation is very underused.