The physical property that describes the amount of matter contained in an object is called mass. Mass is a fundamental characteristic of matter that quantifies how much substance is in an object, typically measured in kilograms or grams. It is distinct from weight, which is the force exerted by gravity on that mass. Mass plays a critical role in various physical phenomena, including inertia, which is the resistance of an object to changes in its state of motion. Understanding mass is essential in fields ranging from physics to chemistry.