In a vacuum tube, which electrode emits electrons?

In a vacuum tube, the cathode is the electrode responsible for emitting electrons. It is typically heated by a filament, which gives the electrons enough energy to escape the metal surface through a process known as thermionic emission. The plate (or anode) is the positively charged electrode that attracts and collects these emitted electrons. The grid is used to control the flow of electrons between the cathode and the plate. A "collector" is a term used for modern bipolar junction transistors, not traditional vacuum tubes.