Cathode / ˈkæθəʊd/ (Greek kathodos – lowering; return, kata – down and hodos – path, movement) – 1) the negative electrode of a chemical current source. 2) The electrode of the device (apparatus) to which the negative pole of the electric current source is connected. 3) Source of electrons in electronic vacuum devices. Depending on the type of electron emission, electrons are distinguished: thermionic, photoelectronic, cold, etc. are divided into types