How can mass be defined?

Mass is fundamentally defined as the amount of substance in an object. It represents the quantity of matter contained within that object, which remains constant regardless of location or the effects of gravity. This concept is crucial in physics and engineering because mass measures an object's inertia, which is its resistance to changes in motion.

Understanding mass as the amount of substance helps differentiate it from weight, which is a force dependent on the gravitational pull acting on that mass, and thus can change based on location (for instance, it would be different on the Moon compared to Earth). Similarly, volume, which measures the space an object occupies, is not synonymous with mass, as different materials can have the same volume but different masses due to differing densities. Recognizing these distinctions reinforces the principle that mass is an intrinsic property of matter, making option C the correct definition.