Definition - What does Train mean?
Train is a a term for a group sex position involving multiple people whose sexual acts connect their bodies in a train-like fashion. The participants involved in a train may be engaged in oral sex, analingus, anal sex, or penis-in-vagina intercourse. The participants in a train may be of any gender or sexuality.
A train can also be called a sex train. Running a train is also a common slang used to indicate that a person has sex with multiple people, one after the other.
Kinkly explains Train
There are many different varieties of train depending on the sexual activity involved. For example, an Oral Train sees people lying on their sides, giving oral pleasure to the person in front of them on the train. An anal train sees people in a line giving and receiving anal sex. An anal train most commonly involves a group of men, but may involve a woman at the start of the chain, or other women using strap-on dildos. A rim train involves a group of people rimming one another.
A train may be performed in a line or in a circle. The activity involved in the line may dictate the preferred formation. If the train takes place in a line, the people at the ends of the line may vary their sexual activities for greater satisfaction. For example, a man at the start of an anal train line may masturbate while receiving anal sex.