pendent jurisdiction

Definition from Nolo’s Plain-English Law Dictionary

In federal procedure, a federal court's right to decide a claim it would not ordinarily have a right to decide, because that claim arises out of the same incident as a claim that is properly before the court. Federal courts are courts of limited jurisdiction, and they generally don't have the right to decide issues of state law between residents of the same state. If, however, a plaintiff sued and alleged both federal and state law claims, the federal court could decide the state law claims under the doctrine of pendent jurisdiction.

Definition provided by Nolo’s Plain-English Law Dictionary.