As used in sections 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.