The option to look at your first 2 cards, double your bet, and stand.
A Double Up Blackjack rule. In exchange, the dealer stands on 16, and then everything except 21 pushes. Example: DU with hard 18 or more, or A-7 or more, against the dealer's weak cards (DU is never best with 17 or less). You can DU only on your first 2 cards, and not on a blackjack.