when having sexual relations with more than one partner at one time, having the two or more "recievers" laying on top of one another so that you can visit each "floor" as you would if you were riding an elevator.
Are you girls ready for my elevator ride? 2nd floor, Suzie. 1st floor, Karen. I'll spend some time in Karen's Basement, then proceed to Suzie to get a nice view of the scenery.