One Touch is a financial game based on on touch option which is a type of exotic option that gives a player a payout once the price of the underlying asset reaches or surpasses a predetermined barrier.
This type of game allows the player to set the position of the barrier, the time to expiration and the payout to be received once the barrier is broken. 
Only two outcomes are possible with this type of option:
1) the barrier is breached and the player collects the full payout agreed upon at the outset of the contract, or
2) the barrier is not breached and the player loses the full premium paid to the broker.

This type of option game is useful for players who believe that the price of an underlying asset will exceed a certain level in the future, but who are not sure that the higher price level is sustainable.
Because a one-touch option only has one barrier level, it is generally slightly less expensive than a double one-touch option. These types of games are becoming more popular with players in the commodity and forex markets.