a threesome:

2 guys and a girl
2 girls and a guy
3 gay guys
2 lesbians

the logistics are a pain in the ass, though

Large, beautiful breasts that are keep well consealed and initially appear to be much smaller and less impressive than they actually are until unleashed.

a heterosexual three-way sex session, involving either two men and one woman or two women and one man; as opposed to a "choo-choo' (which involves three gay men or three lesbians)