Weight = (mass) x (acceleration of gravity at the place where the mass is) .
Man's mass = 80 kg
His weight on Earth = (80 kg) x (9.8 m/s²) = 784 newtons (about 176 pounds)
His weight on the Moon = (80 kg) x (1.63 m/s²) = 130.4 newtons (about 29.2 pounds)
His mass is 80 kg. Mass is the thing about him that doesn't change.
He has the same mass on the Earth, on the Moon, or anywhere.