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In physics, mass (from Ancient Greek: μᾶζα) commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:

- inertial mass,
- active gravitational mass, and
- passive gravitational mass.

Mass must be distinguished from matter in physics, because matter is a poorly-defined concept, and although all types of agreed-upon matter exhibit mass, it is also the case that many types of energy which are not matter—such as potential energy, kinetic energy, and trapped electromagnetic radiation (photons)—also exhibit mass. Thus, all matter has the property of mass, but not all mass is associated with identifiable matter….