Final answer:
A citator is a reference source that enables the researcher to follow the judicial history of court cases.
Step-by-step explanation:
A reference source that enables the researcher to follow the judicial history of court cases is known as a citator.
A citator is a tool used in legal research to find and track the history of court cases. It provides information about the subsequent legal treatment of a case, including whether the case has been overruled or affirmed by higher courts.
For example, a popular citator in the United States is Shepard's Citations, which provides comprehensive information about the judicial history of cases published in the Federal Reporter and Federal Supplement.