Which legal term refers to the practice of using international law derived from customs?

The term that refers to the practice of using international law derived from customs is customary law. Customary law is recognized as a valid source of international law, established through consistent and general practices followed by states, accompanied by a belief that these practices are legally binding. Such customs gain a place in international law when they are widely accepted and adhered to over time, reflecting the behaviors and norms of various nations in their interactions.

This concept is significant because it allows for the evolution of international law based on the realities of state behavior rather than strictly written treaties. The principles of customary law complement conventional law, which is based on explicit agreements or treaties among states. Understanding customary law is essential for interpreting and applying international legal standards when written agreements may not provide sufficient guidance.