A material is a substance or mixture of substances that constitutes an object. Materials can be pure or impure, living or non-living matter. Materials can be classified on the basis of their physical and chemical properties, or on their geological origin or biological function. Materials science is the study of materials, their properties and their applications.

In common usage and classical mechanics, a physical object or physical body is a collection of matter within a defined contiguous boundary in three-dimensional space. The boundary surface must be defined and identified by the properties of the material, although it may change over time. The boundary is usually the visible or tangible surface of the object. The matter in the object is constrained to move as one object. The boundary may move in space relative to other objects that it is not attached to. An object's boundary may also deform and change over time in other ways.