If 3 movies is called a trilogy what is four or more?

Quadrilogy is a nonce Word in which does not exist in the English language.

Nonce Words frequently arise through the combination of an existing Word with a familiar prefix or suffix, in order to meet a particular need (or as a joke). The result is a special kind of pseudo Word: although it would not be found in any dictionary it is instantly comprehensible.

The correct term for a Trilogy in which a 4th title has been added to the works would be called a "Tetralogy"

As an alternative to "tetralogy", "quartet" is sometimes used, particularly for series of four books. The term "quadrilogy", a nonce Word basing the prefix on latin prefix quadri- instead of the Greek prefix, and has also been used for marketing series of movies, such as the Alien series and Die Hard series.

aaannnyyways.. lol either term works to get the point across.. just as long as your not writing a paper that will be graded. :P

---Brian H