In the context of BDSM and the cuckolding kink specifically, a "bull" is a man who becomes involved with a couple to have sexual relations with one partner, typically the woman. In contrast, the other partner (usually the man) watches or is aware but does not participate sexually. The term can also apply to same-sex couples. The dynamic is consensual among all parties and is a form of power play or humiliation for the "cuckold," the partner not involved in the sexual activity.