Think of an actual train - one goes over the tracks, and then another. Now, say these trains were friends of some asshole, and the tracks were... you get the idea.
By Drucill
Run Train
When a bunch of guys have sex with the same girl one after another with no break for the girl
Yo tonight were going run train on that bitch Jenny -Cool hopefully i'm not the caboose.
"Bitch if you don't leave RIGHT NOW me and BoVice gonna run train on you!"
By Angelica
Running Train
when more then 2 males take turns fucking 1 female, inducing multiple orgasms for the female is a must, and it must last a minimum of 2 hours, the males must not have a dick smaller then 6" (the effects of "running a train on a hoe" would be severely weakened by ones with inferior sized cocks) so that by the end of the experience the female is utterly destroyed and sore (maybe even a little bloody) yet usually not regretting her decision.