To make a second wager following a first one. The loser of the first wager will either owe the winner of the first wager double the original bet (if he loses again) or nothing (if he wins).
Fred and Raul bet $10 on a ping pong game. Fred won the first game, so Raul owes him $10. Raul offers "double or nothing." Fred accepts. If Fred wins again, Raul owes him double the original bet ($20). If Raul wins the second game, they are even and he owes Fred nothing.