What term describes a measure of the size of a body or region in three-dimensional space?

The term that describes a measure of the size of a body or region in three-dimensional space is volume. Volume quantifies the amount of space an object occupies and is typically measured in cubic units, such as cubic centimeters or cubic meters. This is an essential concept in geometry and is used in various applications, from calculating how much liquid a container can hold to understanding the capacity of three-dimensional objects.

In comparison, area measures the size of a two-dimensional surface and is expressed in square units. Density refers to the mass of an object divided by its volume, giving a measure of how compact or concentrated matter is within a certain volume. Mass is a measure of the amount of matter in an object and is typically expressed in grams or kilograms, but it does not specifically relate to three-dimensional space. Hence, volume is the most appropriate term for describing the size of a three-dimensional body or region.