At ground level, if you put a 1 kg mass on a scale, and if the scale reads 1 kg, then at this altitude, weight is equivalent to mass. At any higher altitude, the scale will show less weight, but the mass will remain 1 kg. When in orbit about the Earth, the weight of the same mass will be 0 kg, but its mass will still be 1 kg.
In other words, mass is the amount of matter in a body, and weight is the pressure that this mass applies against any obstacle that prevents it from reaching the ground, and when on the ground, it applies a pressure equivalent to 1 kg against the ground.