The German word zwischenzug means 'in-between move', and it is a common tactic that occurs in almost every game of chess! It is also known as an `intermezzo`.
Picture your opponent making a move that directly threatens one of your pieces: instead of responding directly to the threat, you make another even more forcing move, like a check or mate threat.
You expect the normal recapture on e2 isn't it. But 2.Nxe7+! wins a pawn because black is in check 2...Kh8 3.Rxe2. White is a pawn up.