As used in this subchapter:
1. Penal institutions. "Penal institutions" includes a jail, prison, penitentiary, house of correction or other place of penal detention.
2. State. "State" includes any state of the United States, the District of Columbia, the Commonwealth of Puerto Rico and any territory of the United States.
3. Witness. "Witness" means a person who is confined in a penal institution in any state and whose testimony is desired in another state in any criminal proceeding or investigation by a grand jury or in any criminal action before a court.