“Witness” as used in this article shall include a person whose testimony is desired in any proceeding or investigation by a grand jury or in a criminal action, prosecution or proceeding. The word “state” shall include any territory of the United States and the District of Columbia. The word “summons” shall include a subpoena (both subpoena ad testificandum and subpoena duces tecum), order or other notice requiring the appearance of a witness or production of documents.