Acronym for a very famous internet community called "Feet Under The Table", aimed to those whom enjoy playing (with their partner) with feet under the table in public places. Founded 26th July of 2001 by Nyllover, on Yahoo Groups, it then expanded to its own site and forum. FUTT because a very common word to refer to that community, as the name was a bit too long.
I've seen it on FUTT.
He shared them on FUTT.