To "run a train" in sexual terms means that a group of
men wait to have sex with one girl. Usually it does not qualify as a train unless there are more than 7
men involved but the term train is used to describe any number that is more than 1 with a female. The female has sex with a man and after he cums another man enters the room to have sex with the female and so forth. It is only considered a train when the
woman is fully aware of the situation and allows for the
men to have sex with her. Otherwise it would be considered
rape.
Differs and is often confused with gang bang. Train involves sex with one person at a
time while gang bang is when a group of males having sex with a female at the same time.