A more thorough explanation:

Definition: Perfidy is a term used in international law to describe a combatant's deceptive conduct that creates the impression that an adversary is entitled to protection under international law, when in fact the conduct is a ruse to gain an advantage.

Examples of perfidy include:

• Feigning an intent to negotiate under a flag of truce
• Feigning protected status by using signs, emblems, or uniforms of the United Nations or of a neutral country

These examples illustrate how a combatant may use deceitful tactics to gain an advantage in a conflict. By pretending to negotiate or by using symbols of protection, the combatant is able to gain the trust of their adversary and potentially launch a surprise attack or engage in other harmful actions.