In everyday language, we say that the weight of an object is the number of grams of kilograms it… weights!
But the physicians call the number of grams or kilograms the "mass", the weight being the force of gravity induced by the earth mass: P=mg, in Newtons if m is in kilograms and g in meters per seconds to the power 2.
What does that holly mess mean? Are we completely wrong when we speak of the number of kilograms as of the weight?
As a matter of fact, the weight on the earth is equivalent to the mass, as they are proportionnal to one another by the constant g.
The difference can only be seen if we go outside the gravity field of the earth, for instance on the moon: the gravity acceleration g_moon is about 6 times lower than the gravity acceleration g of the earth.
A person, say Neil Armstrong, has the same mass in kilograms on the earth and on the moon, but he is is about 6 times lighter on the moon than on the earth!
But do not be jalous of that magic diet, he will recover his initial weight when he goes back to earth…