Hope this helps
MZFW - Maximum weight allowed before usable fuel and
other specified usable agents must be loaded in defined sections of the aircraft as limited by strength
and airworthiness requirements.
MTW - Maximum weight for ground taxi as limited by aircraft
strength and airworthiness requirements. (It includes weight of taxi and start-up fuel.)
MTOW - Maximum weight for takeoff as limited by aircraft
strength and airworthiness requirements. (This is the maximum weight at start of the takeoff run.)