Hey evilroy,
Quotation from ASA Dictionary or Aeronautical Terms:
"Gross weight (aircraft specification). The loaded weight of an aircraft. Gross weight includes the total weight of the aircraft, the weight of the full and oil, and the weight of all the load carrying."
To me the Max gross weight means, in that case, the maximum weight for the phase of flight. In other words, For take off your maximum gross weight allowed is equal to your MTOW, but for Landing your maximum gross weight will be less.
Sorry if it is not complete. Anyone anything to add?
ZNA