18   Definitions

In this Part:

number includes a letter of the alphabet.

plate holder, in relation to a number-plate, means:

(a)  in the case of a trader’s plate—the trader to whom the trader’s plate has been issued, or

(a1)  in the case of a special number-plate—a special plate holder within the meaning of clause 21, or

(b)  in the case of any other number-plate—each registered operator of the registrable vehicle in respect of which the number-plate has been issued.

vehicle number-plate means a number-plate other than a bicycle-rack number-plate.