"ace up one's sleeve"的定义和意义

What is the origin of the idiom "ace up one's sleeve" and when to use it?

The idiom "ace up one's sleeve" or "card up one's sleeve" has its origins in card games, particularly in the practice of cheating or having a hidden advantage in a game of cards. It refers to the act of concealing a valuable playing card (often an ace) in the sleeve of one's clothing to use it to one's advantage during the game. The phrase has since evolved to describe a secret or hidden advantage, plan, or resource that someone keeps hidden and plans to use to gain an advantage in a situation.