A bull is the third party brought into a cuckold relationship, meant to have sex with one partner while the other partner feels both humiliated and turned on. A bull is generally seen as a more attractive, better endowed, sexually virile man with incredible sexual talents.
Cuckolding is a fetish that is frequently depicted as the woman, (the hotwife) of a heterosexual couple engaging in sex with another man, the bull. Her own male partner, the cuck, is aware of this sexual relationship, and is sometimes a non-touching participant who derives pleasure from the degradation of seeing his partner be better satisfied with a more attractive and sexually competent male.
The bull may also verbally humiliate the cuck while having sex with the hotwife, bragging about his abilities to please her better than the cuck can. While this is the most frequently regarded version of a cuckold relationship and bulls are usually male, any person regardless of gender or identity and relationship dynamic can participate in cuckold fetish.
A cuckold fetish is frequently considered a type of dominance/submission play, with the bull considered more of a tool to facilitate that play for the couple. Even if the bull is dominant in performance, their participation is a means to an end for the cuckold couple.
A bull may also be called a cuckold bull, a swinger bull, or an alpha male, although this term isn’t used exclusively to describe bulls.