Wiktionary
n. (context film English) A film that shows, or purports to show, the actual deliberate killing of one of the performers.
Wikipedia
A snuff film, or snuff movie, is "a movie in a purported genre of movies in which an actor is actually murdered or commits suicide". It may include a motion picture genre that depicts the actual murder of a person or people, without the aid of special effects, for the express purpose of financial exploitation, but that detail is extraneous, so long as it is "circulated amongst a jaded few for the purpose of entertainment". Some filmed records of executions and murders exist, but these were not staged for commercial purposes.
Usage examples of "snuff film".
The only way I could bewitch Eddie would be to show him a snuff film.
I won't tell you what was in the photograph, but the person who wrote the letter said the needle had been used in a snuff film.
An out-and-out snuff film you could rent for three bucks most anywhere.
What he couldn't stand was the fear that that time he had been maneuvered into working on a snuff film.
In fact, it would be like the snuff film one of his underworld colleagues had once shown him.