What is a one actor play called?

Answer 1

It is a play consisting entirely of one act. The act might consist of a few scenes, but no more than would ordinarily occur in the acts of a longer play.
A "one act play" is literally a play in only one act. Usually, plays have 2 or 3 acts, so one acts are shortened and generally very simple plays. They include all the elements of a regular play, they are just much more concise.

Answer 2

A play for a single actor is called a monologue.

Answer 3

An entire play that only contains one act. Act - a series of scenes that creates an act.

Answer 4

A show only involving one actor is generally just referred to as a one-person show (or one-man/one-woman show).

Answer 5

Usually a One Man Show.

Answer 6

monodrama