A one-act play is a type of play which does not necessarily consist of one act. It is neither an act from full length play. More specifically you can say that the duration of the play may be equal to the time normally required by an act from a full-length play.
A one-act play is an independent as well as a self-sufficient form of art. It also consists of all the elements that you find in a full-length play such as setting, characters, property, stage, conflict, and point of view, theme etc. It also has an organic form with beginning, middle and an end. Unlike a full-length play, the unity of time, place and action do not function fully.
You will see that a one-act play does not have episodic subjects; rather it has a visionary and conceptual unity. It normally represents a single situation, action, and atmosphere leading to deep impression. The characters and the experiences are not complex, you can understand easily.
Since it has a confined canvas, the life experiences it conveys can not be complex and difficult as it happens in a full-length play. The number of characters is bound to be small. Some of the beautiful examples that you will love to read are Donne Byrne’s The Professors, Stanley Houghton’s The Dear Departed, and W. W. Jacobs’s The Monkey’s Paw.
Though the orchestral representation, multidimensional experience, a throbbing effect may not be there in a one-act play, but it certainly has to offer a slice of life as a piece of literature does.