Ace in the Hole
Ace in the Hole is a slang expression meaning a secret or extra asset to assure success, referring to the ace playing card a player has as a hole card (or face down card) in a game of stud poker.
In a stud game, having an ace as one's down card or one of one's
down cards.
This being a desirable condition, the phrase passed into general
usage as an advantage or
resource kept in reserve until an opportunity presents itself.
