What is the meaning of gross mass?
It usually refers to the mass of an object together with its container. For example the gross mass of a tin of soup will be the mass of the soup plus the mass of the tin. As a consumer, you will probably be interested in only the net mass - the mass of the soup - but for the haulier it is the gross mass that matters.
For something like breakfast cereal the mass of the container may well be a significant proportion of the gross mass.
In Physics "Mass" and "Weight" are different terms. Mass is a measurement of the amount of matter something contains, while Weight is the measurement of the pull of gravity on an object. Near the surface of the Earth, the acceleration due to gravity is approximately constant; this means that an object's weight is roughly proportional to its mass. So "Gross Mass" and "Gross Weigth" is the same, its just a matter what to use to…
The conversion is not a simple mathematical exercise. You need to know the mass of the container. For example, a truck with a load of 10 tons might have a mass of 12 tons - the additional 2 tons being the mass of the [empty] truck. In that case, the gross mass is 12 tons and the net mass is 10 tons.
Essentially, through semantic shift, although strangely, it has returned, in one sense, to something like its original meaning, one of which was "coarse (of mind)" from the Latin grossus. The modern use is thought to have originated from US university slang from terms such as "gross stupidity". Gross still retains its meaning of large, and in acounting usage (gross and nett profit) and of a dozen dozen.