A sub-genre of Interactive Fiction that deals mostly with "adult" material, namely sex.
While it once became semi-popular with the hacker crowd with the release of xtrek, it has now faded into relative obscurity.
The AIF community currently revolves mostly around the three headed god which is the AIF Portal(http://aif.emsai.net), SAIFA(http://saifa.emsai.net) and the alt.games.xtrek newsgroup. About two to three new games are released each month. Some are cheap smut, while a surprising number of them is actually quite good.