A building, room, or outdoor structure for the presentation of plays, films, or other dramatic performances. A room with tiers of seats used for lectures or demonstrations: an operating theater at a medical school. Dramatic literature or its performance; drama: the theater of Shakespeare and Marlowe. The milieu of actors and playwrights. The quality or effectiveness of a theatrical production: good theater; awful theater. Dramatic material or the use of such material: "His summation was a great piece of courtroom theater\u201d ( Ron Rosenbaum). The audience assembled for a dramatic performance. A place that is the setting for dramatic events. A large geographic area in which military operations are coordinated: the European theater during World War II.