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. Cathodes are commonly found in batteries, where they play a crucial role in the energy storage and release process. In a vacuum tube, the cathode emits electrons when heated, allowing for the flow of current. This principle is essential in devices like cathode ray tubes used in older televisions and computer monitors. Understanding cathodes is vital for grasping how various electronic devices function.