In modern science, weight and mass are different concepts. Weight is the force with which a body acts on a horizontal support or vertical suspension. Mass is a measure of the body's inertia.
Mass is measured in kilograms and weight in newtons. Weight is the product of mass and acceleration due to gravity (P = mg). The weight value (with a constant body mass) is proportional to the acceleration of gravity, which depends on the height above the earth's (or other planet's) surface. And if, more precisely, weight is a particular definition of Newton's second law - force is equal to the product of mass and acceleration (F = ma). Therefore, it is calculated in Newtons, like all forces.
Mass is a constant thing, and weight, strictly speaking, depends, for example, on the height at which the body is located. It is known that with an increase in altitude, the acceleration of gravity decreases, and the weight of the body accordingly decreases, under the same measurement conditions. Its mass remains constant.
For example, in conditions of weightlessness, all bodies have zero weight, and each body has its own mass. And if at rest of the body the readings of the weights are zero, then when the body weights are hit with the same speeds, the impact will be different.
Interestingly, as a result of the Earth's diurnal rotation, there is a latitudinal decrease in weight: at the equator it is about 0.3% less than at the poles.
Nevertheless, a strict distinction between the concepts of weight and mass is accepted mainly in physics, and in many everyday situations the word "weight" continues to be used when in fact we are talking about "mass". By the way, seeing the inscriptions on the product: "net weight" and "gross weight" do not be alarmed, NET is the net weight of the product, and GROSS is the weight with packaging.
Strictly speaking, when going to the market, referring to the seller, one should say: "Please, kilogram, please ..." or "Give me 2 newtons of doctor's sausage" :))) Of course, the term "weight" has already taken root, as a synonym for the term "Mass", but this does not eliminate the need to understand that they are not at all the same thing.