Open has two main meanings, depending on the game. In poker, to open is to make the first bet in a betting round. The player who does it is opening the action, which is where the term comes from. In draw games such as jacks-or-better draw, a player needs at least a pair of jacks to open. In Hold’em, the first player to raise before the flop is said to open the pot, a move known as an open-raise.
In keno, the game is open while the casino is accepting bets on the next draw. Once betting closes, the numbers are drawn. Either way, the meaning is close to the everyday one. Online keno and live game shows present the same idea as a betting window with a countdown timer, and operators set its length to balance pace and participation.