One of the various phrases used to describe the act in which a woman rubs her vulva against her partner's body for the purpose of sexual pleasure. In this case, an Oyster Clamp occurs when the lips are sticking due to the lack of lubrication and are firmly pressed together so that they become interlocked or "clamped."

see also:
scissoring

A casual invitation / threat used by an individual that is not afraid of fucking someone up.