Sexual intercourse.

The actual expression is hundreds of years old, and was made famous by Shakespeare in Othello.
BRABANTIO: What profane wretch art thou?
IAGO: I am one, sir, that comes to tell you, your daughter and the Moor are now making the beast with two backs.

(Othello, Act 1, Scene 1).
by Dr Pinch April 12, 2005
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to copulate or partake in coital activity; to do the bone dance; have sex.
The saloon keeper and the town trollop were 'making the beast with 2 backs'like 2 jackrabbits on steroids atop the pool table, after he locked the saloon doors, as the last sot vacated the premises at 3 a.m.
by weave January 9, 2004
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Male homosexual intercourse. Derivation of the Shakespearean reference to traditional male / female intercourse MAKING THE BEAST WITH 2 BACKS.
"Do you think he'd be the type of guy Jen might like?"

"No, I think he and his friend and going to be making the beast with 2 hairy backs later tonight."
by TRex1 April 1, 2006
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