A Theater

1. A place or building, consisting of a stageand seating, in which an audiencegathers to watch plays, musical performances, public ceremonies, and so on.
2. A region where a particular action takes place; a specific field of action, usually with reference to war.
3. A lecture theatre.
4. (medicine) An operating theatre or locale for human experimentation.
5. (US) A cinema.
6. Drama or performance as a profession or art form.
7. Any place rising by steps like the seats of a theater.

Usage notes

• The spelling theatre is the main spelling in British English, with theater being rare.
• In United States English, theater accounts for about 80 percent of usage in the major corpus of usage, COCA.
• Among American theatre professionals, there is some usage of the two spellings in order to differentiate between the location theater (as in definitions 1-5) and the art-form theatre (definition 6). A variant of this differentiation is the usage of theatre for things relating to live performances (as in definitions 1 and 6) with theater being used for all other uses.