Picard holding up an Ace
An ace was a playing card featuring a heart, diamond, spade, or club.
In 2365, Worf and Katherine Pulaski played poker; the former won with a full house (three aces and two queens), while the latter lost with a straight. In the following hand of seven card stud, Data called, "After the queen, one-eyed jacks and low card in the hole are wild." (TNG: "The Emissary")