A stratagem whereby you can trap an opponent’s trump honour without taking an actual finesse.
With spades as trumps, you lead a heart from dummy. Whatever East does, you overruff and make the last two tricks.
To reach a position like this you need to ensure that you have the same number of trumps as the defender (if you had more, you would have to ruff and lead away from your trump holding). You will also need to ensure that the lead is not in the hand with the trump tenace.