Mass is both a property of a physical body and a measure of its resistance to acceleration (a change in its state of motion) when a net force is applied.^[1] It also determines the strength of its mutual gravitational attraction to other bodies. The basic SI unit of mass is the kilogram (kg). In physics, mass is not the same as weight, even though mass is often determined by measuring the object's weight using a spring scale, rather than balance scale comparing it directly with known masses.[...]

(Wikipedia)