What is a group of four called?

There isn't one definitive word for a group of four. It depends on what the group is composed of. Here are some options:

* General:

* Quartet (used for musical groups)

* Quadruplet (referring to four identical things)

* Group of four (simple and straightforward)

* Specific:

* Foursome (for a group of people, often in a game like golf)

* Quadrangle (for a group of four buildings)

* Tetrad (for a group of four related objects)

* Four-in-hand (for a group of four horses)

The best term to use will depend on the context of the group.