From the transport
SA website:
# Gross Vehicle Mass or GVM of a vehicle means
(a) the maximum loaded mass of the vehicle-
(i) as specified by the vehicle’s manufacturer; or
(ii) as specified by the Registrar if -
(a) the manufacturer has not specified a maximum loaded mass; or
(b) the manufacturer cannot be identified; or
(c) the vehicle has been modified to the extent that the manufacturer’s specification is no longer appropriate
or
(b) the unladen mass of the vehicle (if neither the vehicle’s manufacturer nor the Registrar has specified the maximum loaded mass of the vehicle
link here
Tare Weight:
This is the weight of the unladen vehicle, i.e. the weight you will use to calculate the vehicle's load.