A trilogy.
They call it a dilogy or duology.
pentalogy
tetralogy
A trilogy
3
Decalogy
Yes there are 2- 3 books in the series
Trilogy
Their are 3 ordinary boy books
There are four books in the Brixton Brothers series written by Mac Barnett.
By analogy of the word "trilogy" for a series of 3 books, a single word for a series of 5 books would be a "pentalogy". This word is derived from the greek: 'penta' (meaning "five") and '-logy' (from "logia" - for which one meaning is "a collection of words").
There are five books in "The Sisterhood of the Traveling Pants" series by Ann Brashares.