look up any word, like darude - sandstorm:
 
1.
Alternate sex partner being seen as the same time as another.
I have one girlfriend and 3 side-fucks.
by Emi, Will, Hunter December 07, 2006
 
2.
The act of creating a new orifice in a person's side, and then raping the person using the new hole.
"Billy was mad at Timmy because Timmy had cut off Billy's left nut in a prank gone wrong, so Billy used his pocket knife to cut a hole in Timmy's abdomen, then sidefucked him. Timmy learned his lesson"
by cheesegrass September 04, 2007