In movie-making parlance, a threequel is a sequel to a sequel, the third in a series of similarly-themed films that include one or more of the same characters featured in the first two.
The following films are examples of a threequel not listed in the prior definition:
Rocky III (1982)
Friday the 13th Part 3 (1982)
Halloween III: Season of the Witch (1982)
Superman III (1983)
Jaws 3-D (1983)
Smokey and the Bandit Part 3 (1983)
Star Trek III: The Search for Spock (1984)
The Muppets Take Manhattan (1984)
Police Academy 3: Back in Training (1986)
A Nightmare on Elm Street 3: Dream Warriors (1987)
Rambo III (1988)
The Karate Kid, Part III (1989)
Leatherface: Texas Chainsaw Massacre III (1990)
The Godfather Part III (1990)
The Exorcist III (1990)
Back to the Future Part III (1990)
Lethal Weapon 3 (1992)
RoboCop 3 (1993)
Naked Gun 33 1/3: The Final Insult (1994)
Die Hard with a Vengeance (1995)
Batman Forever (1995)
Scream 3 (2000)
Jurassic Park III (2001)
Austin Powers in Goldmember (2002)
The Lord of the Rings: The Return of the King (2003)
The Matrix Revolutions (2003)
American Wedding (2003)
Mission: Impossible III (2006)
The third installment of a legacy or trilogy.
Lord of the rings: The fellowship of the rings
Lord of the rings: The two towers
Lord of the rings: The return of the king
The third in a series, as in movies or literature.
I am excited about the upcoming threequel to Ghostbusters!
The third movie in a series.
Guy 1: The new Transformers movie seems like an awesome threequel.
Guy 2: Yah, but there's no Megan Fox.