A cathode is an electrode through which electric current flows into 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, allowing it to release energy. In electronic devices like vacuum tubes and cathode ray tubes, the cathode emits electrons when heated or subjected to a strong electric field. These emitted electrons then travel towards the anode, creating a flow of current. The behavior of the cathode is essential for the operation of many electrical and electronic systems.