California Vehicle Code definition of
CVC Section 233. (a) Except as provided in subdivision (b), a "bus" is any
vehicle, including a trailer bus, designed, used, or maintained for
carrying more than 15 persons including the driver.
(b) A vehicle designed, used, or maintained for carrying more than
10 persons, including the driver, which is used to transport persons
for compensation or profit, or is used by any nonprofit organization
or group, is also a bus.
(c) This section does not alter the definition of a schoolbus,
school pupil activity bus, general public paratransit vehicle, farm
labor vehicle, or youth bus.
(d) A vanpool vehicle is not a bus.