snuff film

A fetish film, sometimes pornography, in which the slow process of someone being tortured and killed is committed to video tape. The basic snuff film has a subject, usually an abductee, who is tortured with various instruments of mutilation for most of the duration of the film. The film often ends with the final "snuffing" of the victim in a savage orgy of carnage (sometimes chainsaws are used). By this time he/she may already be disemboweled and the chest cavity may be fully open (before the victim is finally snuffed), and the other participants may commit acts of further perversion with the vital organs of the victim.
The unreleased Broken movie by Nine Inch Nails was reported to contain clips from a snuff film, prompting authorities to conduct an investigation.

According to the FBI, snuff films are an urban legend. They may exist, but the FBI has yet to find any authentic ones. "Snuff" films are fakes passed off as or mistaken for the real thing. Nicholas Cage watches a lot of these fakes in 8mm, and even most of the porn freaks he talks to say there's no such thing.

Nine Inch Nails's unreleased long-form video for the EP broken was a take on a snuff film. It's not real, but it's really grainy, and, unlike The Blair Witch Project, actually increased the feeling of reality while watching the film.

Really, really, really, graphic stuff. Faces of death, even the non-faked scenes, ain't got nothin' on this.

For a more hi-fi and artsy type, see Bob Flanagan in the video for NIN's Happiness in Slavery. Flannigan is also the focus of the biographical documentary "Sick" (full title: Sick: The Life & Death of Bob Flanagan, Supermasochist), which you can find at better video stores near you. It's actually a very interesting look at the relationship between Bob and his wife (who did many of the acts upon him). Mr. Flanagan passed away from Cerebral Palsy (I think). I'll double check that and update later.