Buck is a term used in some BDSM dynamics to describe a third partner—typically a man—who has sex with the knowledge, consent, and often participation or presence of their partner (the stag).
Unlike a bull, who may be dominant and assertive, a buck is generally viewed as a guest in the dynamic: invited, respectful, and deferential to the couple’s boundaries. His role is about pleasure and shared experience, not control or humiliation. In this context, the buck complements the couple rather than taking center stage.
Alternatively, this can simply be slang to refer to a younger, attractive male.
