Consensual non-consent (CNC for short) is a form of sexual role-play where one of the willing partners is going to resist the sexual activity; part of the thrill for that person is being overpowered and forced to do something against their will. They may fight back, try to get away, tell their partner to stop, even though they don't actually want their partner to stop because it's all part of the role-play. The purpose of a safeword is to have an unambiguous word (almost always non-sexual, e.g. "pineapple") the resisting partner can use to indicate they really do want the activity to stop.