The definitions in Part 3 (commencing with Section 20000) shall apply to this part. The following definition shall also govern the interpretation of this part:
“Participating agency” means any public agency that meets the criteria for becoming a contracting agency in this system pursuant to Chapter 5 (commencing with Section 20460) of Part 3, but that has not elected to participate in this system as a contracting agency, and that elects to contract with the board to participate in the replacement benefit plan administered pursuant to this part by the board.