What is a Theater?

Theater is a way of expressing yourself. By using your role, you can handle the situation by how you would have handled it
Theatre can be precisely defined as

A does B for C

A=Performer

B=Action

C=Audience

therefore, anything can be theatre.

Drama, however, is a special kind of theatre

A does B as D for C

A=Performer

B=Action

C=Audience

D=A Character