It stands for double one-touch option; a one-touch option with two American barriers. An investor, buying the option, has the right to define the two barriers: one above and one below the underlying. If the underlying breaks out the range bounded by the two barriers, a fixed payout will be received by the option’s buyer on the expiration date.

If neither of the two barriers is “touched” or broken through, there would be no payout (payoff is zero).