As used in this chapter, unless the context otherwise requires:
 1. “Board” means the board of supervisors of a county.
 2. “Book”, “list”, “record”, or “schedule” kept by a county auditor, assessor, treasurer, recorder, sheriff, or other county officer means the county system as defined in section 445.1.
 3. “District” means a benefited emergency medical services district.
 4. “Trustee” means a trustee of a district.