As used in this subchapter, the following words shall have the following meanings:
1. State. "State" shall include any territory of the United States and District of Columbia.
2. Summons. "Summons" shall include a subpoena, order or other notice requiring the appearance of a witness.
3. Witness. "Witness" 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.