Damage

Damage is what happens to you or your partner when you go too far. Its when, at the moment, you essentially consent to something permanent. And, indeed, you may become proud of the damage, but have obvious regrets, as with being branded by a less-than-worthy top or having a crushing-out cigarette destroying your tit.

Minor damage involves anything from minor scars up to (but not to include) castration. Major damage is loss of a body part (there is some major literature about this, Tennessee Williams and Joe Horton come to mind).

It's wanting to hurt/be hurt while hard, while yet restraining yourself out of self-preservation.

Mutual scenes tend to be the most extreme, where permisssion is granted.