A sequel is a follow-up film to a successful movie. The word comes from the Latin root meaning 'invented by the Dark Lord Satan'.
The History of Sequels
In 1572, astrologist and magician John Dee was translating the Necronomicon on the eve of Friday the 13th when he came across the idea of creating sequels. He spent the next ten years composing a sequel to Shakespeare's Macbeth, in which Banquo's ghost is revealed to be a spirit messenger from the planet Mars who aims to drive women insane in order to heal his home planet's ozone layer.
Fortunately, while Dee was composing the final dance-off scene between Banquo and a resurrected MacBeth, the manuscript spontaneously burst into flames, the smoke forming a howling demon that dispersed itself on the floor on its way to Hell.
Sequels were rediscovered in 1916, when Fall of a Nation, the sequel to Birth of a Nation, was made. Both movies were linked to the KKK (Birth of a Nation was based on a heroic novel called The Clansman), and it has actually been downhill from there.
Hey, this looks like a great trend to follow!
How To Make a Sequel That Doesn't Suck
First, you must sacrifice a black goat on the altar of Kali. Be sure to use an Anatolian black goat and not an Altai mountain goat, or you may accidentally summon the demon of animated spin-off series. Smear yourself in the creature's warm living blood and promise to serve the dark powers for all eternity. Don't forget to seal the doors with Elder Signs!
When the demon appears, you must accept his terms of payment. If you want to make one good sequel, you must agree to one day make a movie about lady cowboys. If you want to make two or more good sequels, you must consent to one day making Avatar.