Leakage current is the unwanted flow of electrical current in an insulating material or a semiconductor when it's supposed to be in an off or non-conductive state. It's a critical parameter in electronic devices, as excessive leakage can lead to power loss, reduced efficiency, and potential device failure. For example, in a transistor, leakage current can affect the switch-off capabilities, impacting the overall performance of the circuit. Minimizing leakage current is essential for the reliability and energy efficiency of electronic systems.