It's a total of the 3 cards showing just after the deal. Your 2 cards (cards dealt face up at this table) and the dealer's up card. My total of 14 + his 5 showing = 19 and a 1 to 1 payout.

I'd really like to see the math on this bet! It seems to be an interesting bet, but it must have some juicy percentage hold for the house.