Final answer:
The law that is derived from a court decision is known as Common law, which develops through court decisions and creates precedents that guide future rulings and ensure legal consistency.
Step-by-step explanation:
The law derived from a court decision is known as A. Common law. Common law, also referred to as case law or precedent, is developed by judges through decisions made in court, as opposed to statutory law which is established through legislative processes. Judges, when ruling on cases, look to precedent—previously decided cases that help guide and justify their current decisions. This practice is called stare decisis, which means "to stand on the decision." Judges apply the rule of law contained in earlier cases to similar current cases, thus ensuring consistency and predictability in the legal system.
Common law plays a critical role in the United States' legal system, where it interacts with statutory and regulatory law, often filling gaps and making the legal system more comprehensive and adaptable to changing circumstances. This form of law is integral to the adversarial judicial system, characteristic of common law tradition, and also informs public policy through the court system, underscoring the judiciary's role in saying what the law is.