A victor gives no quarter when the victor shows no clemency or mercy and refuses to spare the life in return for the surrender at discretion (unconditional surrender) of a vanquished opponent.
Under the laws of war "… it is especially forbidden … to declare that no quarter will be given". This was established under Article 23 of the IV Convention – The Laws and Customs of War on Land of the Hague Conventions of 1907.
Since a judgement on the law relating to war crimes and crimes against humanity at the Nuremberg Trials in October 1946, the 1907 Hague conventions, including the explicit prohibition to declare that no quarter will be given, are considered to be part of the customary laws of war and are binding on all parties in an international armed conflict.
The term originates from an order by the commander of a victorious army that they "will not quarter (house)" captured enemy soldiers. Therefore, none can be taken prisoner and all enemy combatants must be killed.