mass

Definition: A measure of a body's inertia or the amount of matter contained with in the body. The mass standard is a 1-kg cylinder of platinum-iridium alloy. Mass defined this way is called the inertial mass of a body. Mass can also be defined in terms of the gravitational force it produces. The mass defined in this way is called the gravitational mass. Experiments have shown that gravitational mass and inertial mass are indistinguishable.