Mo. Rev. Stat. § 491.400: Definitions.

As used in sections 491.400 to 491.450 the following terms mean and include:

(1) "State" , any territory of the United States and District of Columbia.

(2) "Summons" , a subpoena, order or other notice requiring the appearance of a witness.

(3) "Witness" , a person whose testimony is desired in any proceeding or investigation by a grand jury or in a criminal action, prosecution or proceeding.