What does mass mean in the metric system?

Answer 1

Weight

Technically mass is a body's resistance to acceleration. That means that the greater the mass of a body, the greater the force needed to start or stop it moving. In everyday language mass is referred to as weight, but weight is the force acting on a body, due to gravity normally, and is measured in newtons, mass is measured in kilograms.

Answer 2

The concept of "mass" doesn't just apply to the metric system. The mass is often informally called the "amount of substance". This is not a very precise definition; to be more precise, you can think of mass as a property that provides objects with:

a) Inertia. Objects with more mass are more difficult to speed up or slow down.

b) Gravitational attraction. Objects with more mass also have more weight. (The weight also depends on the gravitational field - on Earth, a mass of 1 kg has a weight of about 9.8 newton.)