When you have a person with a dick (OEM or aftermarket) laying on their back, and one person is riding their dick and another person is riding their face, and they high five and/or kiss, thus creating a triangular shape reminiscent of the Eiffel Tower.
My homegirl and I Eiffel Towered my boyfriend at a New Year's Eveorgy, it was awesome!!
An eiffel tower happens during a ménage à trois, sexual intercourse between three people, where one penetrates another vaginally or anally and the other penetrates the same orally, then the penetrators make a high-five resembling the structure of the Eiffel Tower.
It's a variation of the Eiffel Tower you still have the guy standing getting head and the guy doing the girl in the ass but then you have another guy underneath doing her in the vag the two guys up top slap hands and you have two additional guys getting hand jobs from the woman on the sides.
"So me and the boys Eiffel Tower With A Strong Base And Tourists a bitch after two of her buds came in, whopped their cocks out and became tourists"