vacuum tube types - technical definition

Following are the different types of vacuum tubes and the elements used to control the flow of current.

  Elements       Diode  Triode  Tetrode  Pentode

  Cathode          X      X       X        X
  Plate            X      X       X        X
  Control grid            X       X        X
  Screen grid                     X        X
  Suppressor grid                          X