In professional wrestling a screwjob occurs when a match ends in a controversial finish, often involving cheating or outside interference. This is in contrast to a clean finish, in which the match ends in an untainted manner. This type of finish upsets fans, especially those who have paid to watch a live event or PPV, because it is unsatisfying and does not end a feud.
The Montreal Screwjob was a significant one-time-only occurrence in WWE. See that article for more information.
See also: professional wrestling slang, Montreal Screwjob