The word 'stud' in LGBT-usage is a man who has a well built body and usually plays the top role. The word comes form the agricultural usage of the word which describes an animal that is not castrated, which means that it is capable of producing and offspring. In the usage, the word usually implied hypermasculinity and aggression. In most of the films, studs are expected to do some form of aggressive sexual acts like irrumatio or very powerful anal thrusts.
The term was originally used to describe a farm animal that did not undergo the process of castration. Thus the animal was deemed more masculine than the others. They are capable of producing an offspring and therefore considered to be more fertile. In ancient times, the gods are mainly depicted as studs. Most of the male gods, especially those that belong to the fertility group, are depicted to have horns (which is a phallic symbol) or a very large erect penis.
In gay pornography, studs are often depicted as men with well defined muscles as opposed to bears. Sometimes, they also have some body hairs that in turn distinguish them from the twinks. In some films, they often represent a hypermasculine stereotype of men, like those belonging to the armed services, policemen, firemen or even prisoners.
Aggression and suppression are mainly the themes of movies that depict the stud. In many films that feature studs, the studs tend to overpower his partner (generally a twink). When the bottom performs an fellatio, it is expected that the stud not only receive it but active perform an irrumatio.
Other films, may feature two studs trying to overpower each other. Generally, in these genre, the loser in the battle (which is deemed weaker and lesser masculine) is forced to perform an fellatio or receives a violent anal thrust.
Lately, Brazil has been a prolific source of stud-oriented gay pornographic films.