The in-between check
A tempo move (顿挫) is an in-between check slipped in before the move you really want to play. The check forces a reply, and in that borrowed time the target's circumstances change. Here the black chariot on e8 is guarded by the king on e9: capture now and you only trade. But your horse can jump to d7 with check first — the king must step aside (his own chariot jams e8), and once he leaves the e-file the chariot is guarded by nobody.