Definition & Meaning of "poker face"in English

What is the origin of the idiom "poker face" and when to use it?

The idiom "poker face" originated from the world of poker, a card game where players attempt to conceal their emotions and maintain a neutral facial expression to avoid giving away their hand or intentions. The phrase is used to signify the ability to keep a calm and composed demeanor, showing no visible signs of one's thoughts, feelings, or intentions.