In-Depth Explanation
Optimal when holding 10 or 11 against a weak dealer upcard (4, 5, 6).
A blackjack option to double your original stake in exchange for receiving exactly one additional card.
Optimal when holding 10 or 11 against a weak dealer upcard (4, 5, 6).
Doubling down on 11 against dealer 5; dealt a 10 for 21.