To delope is to fire your gun harmlessly into the air, on purpose, when fighting a duel. It's from French duelling terminology.
If you delope in a duel, it can mean that you are acknowledging that your opponent is in the right. It could also mean that you don't want to kill or wound your opponent for some other reason, though.
In the Code Duello, normally, two shots are exchanged before the duel can be ended honorably. The Code specifically prohibits the delope. But romance novel heroes have been known to delope and get away with their honor intact!