Which term describes a legal system based on judicial decisions and customs?

The term that best describes a legal system based on judicial decisions and customs is common law. This system relies heavily on precedents set by previous court rulings, which judges use to guide their decisions in current cases. The foundation of common law is the principle that past decisions create binding or persuasive authority for future cases, thereby establishing a body of law that evolves over time through the interpretations and applications made by the judiciary.

This contrasts with civil law, which is primarily based on codified statutes and laws that are created by legislative bodies. While statutory law involves legislation passed by governments, administrative law pertains to regulations created by governmental agencies. Each of these alternatives lacks the characteristic of being built primarily on judicial decisions and customs, making common law the most appropriate choice in this context.