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:

Goldfinger (1964)
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)
Alien3 (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)
by ConsocoTutto October 6, 2007
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The third in a series, as in movies or literature.
I am excited about the upcoming threequel to Ghostbusters!
by Jason Patrick Doherty September 21, 2008
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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
by The Addictive Donkey November 26, 2004
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Guy 1: The new Transformers movie seems like an awesome threequel.
Guy 2: Yah, but there's no Megan Fox.
by Sombrero Siesta Fiesta July 3, 2011
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the imaginary third musical in the popular a very potter musical series. it follows a very potter sequel, and many fans have been spamming darren criss' twitter, begging for such a totally awesome show. we don't know if it would follows harry and co., the marauders, or the next generation, but we do know that it's gonna be totally awesome.
person one; "damn, i wish there was a very potter threequel!"
person two; "merlin's pants, i know. that'd be supermegafoxyawesomehot.
by red vines January 24, 2011
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