Poutine is french fries covered in gravy and cheese curds. Don't accept regular cheese as a substitute! Typically, the cheese curds are white, so the don't really look much different in a picture than french fries do after they've been covered in gravy.

FWIW, I've had a lot of Americans ask me if there's any special "Canadian" foods. The only thing I can think of is poutine.

If you ever order it, you'll want to be careful about pronunciation, since a little minor slip can have you asking for... something a little naughtier.