The noun theater has 3 senses (first 2 from tagged texts)
1. (7) theater, theatre, house -- (a building where theatrical performances or motion-picture shows can be presented; "the house was full")
2. (3) dramaturgy, dramatic art, dramatics, theater, theatre -- (the art of writing and producing plays)
3. field, field of operations, theater, theater of operations, theatre, theatre of operations -- (a region in which active military operations are in progress; "the army was in the field awaiting action"; "he served in the Vietnam theater for three years")