As used in section 91 to 95 of this chapter:
  (a) “Witness” includes a person whose testimony is desired in any proceeding or investigation by a grand jury or in a criminal action, prosecution or proceeding.
  (b) “State” includes any territory of the United States and the District of Columbia.
  (c) “Summons” includes a subpoena, order or other notice requiring the appearance of a witness.