Duology vs. Trilogy

(nonstandard) A series comprising two parts, particularly in genre fiction.

A duology (from Latin duo “two” and Ancient Greek λόγος (lógos, “word”) is a series comprising two literary, theatrical, or cinematic works. Despite many films being part of duologies, the term is seldom used outside of literature.

A set of three works of art that are connected, and that can be seen either as a single work or as three individual works. They are commonly found in literature, film, or video games.

A series of three dramas which, although each of them is in one sense complete, have a close mutual relation, and form one historical and poetical picture. Shakespeare's " Henry VI." is an example.

Example: ‘On the Greek stage, a drama, or acted story, consisted in reality of three dramas, called together a trilogy, and performed consecutively in the course of one day.’;

a set of three literary or dramatic works related in subject or theme

A trilogy is a set of three works of art that are connected and can be seen either as a single work or as three individual works. They are commonly found in literature, film, and video games, and are less common in other art forms.