In the game of poker, a card is said to be “in the hole” when it’s hidden from the view of the other players or spectators. A player can receive a card from the dealer, take a glimpse at it, and leave it lying face-down, saving it for a subsequent play. The other players are often left guessing what that card might be, or dreading that it might be an especially potent card. The ace is the most valuable card in the whole deck. So,  if the card that the player has “in the hole,” known in poker lingo as a “hole card,” turns out to be an ace, it could easily guarantee him victory.

That’s why the American expression “ace in the hole” means “information or some kind of resource that is held in reserve and can be used to give one a great advantage in a specific situation.” The phrase “ace in the hole” has been used in the context of poker since the 19th century, but it came to mainstream use after the 1951 movie, “Ace in the Hole” was released. It was about a man who chose to delay saving someone just so he could benefit from reporting on the incident.