The play of a card, or a line of play, with the express intention of deceiving opponents about the true lie of the cards.
If South, the declarer leads a spade from hand and finesses dummy’s nine, East might win deceptively with the king (or queen). Declarer may then waste an entry returning to hand to take a further finesse. If East won the first round of spades with the ten, declarer would know at once that the suit would not run for one loser.