From www.grammarist.com:
There is no difference in meaning between theater and theatre. Neither has any special definitions. Theater is the preferred spelling in American English, and theatre is preferred virtually everywhere else.
Some American writers do make distinctions—for instance, that theater is a venue while theatre is an art form, or that theater is a movie theater while theatre is a drama venue—but these are preferences, not rules, and they are not consistently borne out in real-world usage.
