Lack of personal jurisdiction refers to a situation where a court does not have the authority to make decisions affecting a particular defendant's rights due to insufficient connection between the defendant and the state in which the court is located. This lack of connection can arise when the defendant does not reside in the state, has not consented to jurisdiction, or has not engaged in activities that would establish a sufficient nexus with the state. Understanding personal jurisdiction is crucial because it can determine whether a court has the power to hear a case and enforce its judgments.