A jurisdictional defect refers to a failure of a court to have proper authority to hear and decide a case, which can stem from factors such as lack of subject matter jurisdiction or personal jurisdiction over the parties involved. This defect can result in the dismissal of a case or the inability to enforce a judgment, as the court is not recognized as having the legal power to adjudicate the dispute. Jurisdictional defects are critical in determining the correct forum for a case and ensuring that parties receive due process.