Move a piece and uncover an attack by the long-range piece behind it. Two threats for one move. Discovered check is the killer version: the check is forced; whatever the mover grabs, stays grabbed.
Remember
• Setup: your piece blocks your own long-range piece's line to an enemy target.
• Move the blocker: the long-range piece's threat is revealed.
• Discovered check is the strongest form. Check forces the response.
• Meanwhile the blocker does as it pleases: capture, threaten, anything.