A cathode is an electrode through which electric current flows out of a device. In electrochemical cells, it is the site of reduction, where electrons are gained by ions or molecules. In a battery, the cathode is typically the positive terminal during discharge, where chemical reactions occur to produce electricity. In devices like cathode ray tubes and LEDs, the cathode plays a crucial role in emitting electrons or light. The performance and efficiency of these devices often depend on the materials used for the cathode, which can vary based on the application and technology involved.