How come you guys call it a theatre and not a cinema? Isn't a theatre where you go to see live performances and not films?! Haha there are so many differences in words between our countries, amuses me!
I haven't been to the cinema since the last Harry Potter because it is just so overpriced! I remember when going there used to be a cheap date haha!
It's both. You can say "I'm going to the theatre," or "I'm going to the cinema" or "I'm going to the movies."
When it comes to plays, because it's much more of a rare occurance, you'd say: "I'm going to a play," or "I'm going to the theatre to see a play." You'd probably specify depending on the context.