Having a three some; having sex with 2 people at the same time. This could involve doing home base with the first person and doing third with the 2nd person at the same time. Finger one girl, fuck the other. or if 2 guys, having sex with one and anal with the other. (double home base) or girl is having sex with one and blow jobin' the other.
Last night at the bar, I took these twins back to my place and I hit sixth base with them doggy style