A low card, usually in the dummy, that can become an entry with careful play. Usually declarer plays one or more of his high cards of a suit under the high cards in dummy.
For example, with K-Q-J-4 facing A-5-3-2, the five could be a hidden entry – when crossing to the ace, declarer leads an honour and overtakes, setting up the five as a fourth- round entry on the normal 3-2 break.