The Devil's Coup is a declarer play in contract bridge

Contract bridge

Contract bridge, usually known simply as bridge, is a trick-taking card game using a standard deck of 52 playing cards played by four players in two competing partnerships with partners sitting opposite each other around a small table...

that prevents the defense from taking an apparently natural trump trick - often called "the disappearing trump trick".

Example

A typical example is shown where spades are trumps and the lead is in dummy (North).

The 3 is led. If East ruffs low, then declarer overruffs low and cashes the ace and king of spades. If East ruffs high, declarer overruffs with the K and finesses West for the Q to make the remaining two tricks.
Devil's coups are fairly rare: not only the trump suit but the side suits must lie well for declarer.