An echo question is a question that directly takes up (or "echoes") part of a declarative sentence made before. It copies an utterance and contains a wh-phrase in situ.
A: I'm going to Nizhnesverdlovsk. B: You're going where?
This type of question is usually considered irrelevant in the discussion of wh-movement (What did John buy?) and wh-in-situ (Who bought what?).