Test Process that sources a quantity of matter which a body contains, as measured by its acceleration under a given force or by the force exerted on it by a gravitational field. The term “mass” is always used in the strict Newtonian sense as a property intrinsic to matter. Mass is the proportionality constant between a force on a material object and its resulting acceleration. This property is sometimes referred to as “true mass”, “vacuum mass”, or “mass in a vacuum” to distinguish it from conventional [apparent] mass. The true quantity of matter represented in a vacuum with no gravitational force.