What is "Yaoi?"
Artwork, comics, games, movies, stories, etc. involving male x male relationships of a sexual nature. "Yaoi" is an acronym for "yama nashi, ochi nashi, imi nashi (no meaning)" which translates to "no climax, no point, no meaning"... an old joke is that it's an acronym for "yamete kudasai, oshiri ga itai yo" (stop it, my butt hurts). Yaoi can contain shonen-ai elements (and often does) or it can be purely sexual. The realism of the pairing is irrelevant. Note that yaoi should really only be used to refer to pairings taken from Japanese media and is denoted seme x uke... in the Western culture the proper term would be slash. The female x female equivalent is called "yuri."