What term describes the mass of a substance per unit volume?

The term that describes the mass of a substance per unit volume is density. Density is mathematically defined as the mass of an object divided by its volume (density = mass/volume). It provides a way to quantify how much matter is packed into a given space, which is essential for understanding properties of materials in various scientific disciplines.

For example, knowing the density of a substance allows scientists to differentiate between materials, predict whether objects will float or sink in a fluid, and determine how mass changes as a substance changes state (like ice melting to water). Density is a fundamental property used across many fields, including physics, chemistry, and engineering, to analyze and manipulate materials—making it a vital concept in science.