A blank, emotionless expression that gives no indication of one's thoughts or intentions. Poker players use such an expression so as not to give their opponents any clues about which cards they are holding. I kept looking over to see if she was impressed, but she wore a poker face throughout the performance.Now, make sure you keep your poker face on for these negotiations—we can't let them know where we stand.

Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

A visage lacking any expression that can be interpreted, as in Whenever Betty attended one of her children's performances, she managed to keep a poker face . This term alludes to the facial expression of a poker player who is expert at concealing his feelings about his hand. [c. 1880]

The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Total lack of expression; deadpan. This term comes from gambling, where the astute player tries not to betray the quality of his or her hand by remaining expressionless. Originating in the late nineteenth century, the term was transferred to other areas in which individuals tried hard not to betray their thoughts. C. E. Mulford used it in his western novel, Rustler’s Valley (1924): “He glanced around the circle and found poker faces.”

The Dictionary of Clichés by Christine Ammer Copyright © 2013 by Christine Ammer