In this subchapter:
(1) "Constituent agency" means a public agency that is a party to an agreement under Section 22.072 to act jointly under this subchapter.
(2) "Governing authority" means the governing body of a county or municipality or the head of a public agency other than a county or municipality.
(3) "Joint board" means a board created under Section 22.074.
(4) "Populous home-rule municipality" means a home-rule municipality with a population of more than 400,000.
(5) "Public agency" includes a local government, an agency of the state or of the United States, and a political subdivision or agency of another state.