The terminal on an electrical device from which a major flow of electrons takes place (as in a vacuum tube) or from which electric current flows (as in a battery). The converse of anode. The term is also sometimes used to refer to the negative side of a solid state diode. In tubes the cathode is the source of a cathode-ray, or a cloud of electrons that moves towards the oppositely changed anode. A cathode-ray tube (CRT) is a special case where this is used to generate a picture on a phosphorous screen.