Zwischenzug
A zwischenzug is an in-between move that you play before the recapture or reply the position seemed to require.
The expected move is still there a ply later. You insert a check, a stronger capture, or a threat that the opponent must answer first, then you take back.
White has just captured on d5. Recapturing with the bishop is the obvious reply. Bb4+ is the in-between move: it checks, White must deal with the king, and only then does the bishop situation get resolved — often on better terms.
The coach uses this word when you (or Maia) skip a recapture to give a check. If the check is real, the recapture will still be available.