any property used to characterize matter and energy and their interactions

one of the four quantities that are the basis of systems of measurement

the main mass of a thing

the total mass of living matter in a given unit area

the minimum mass of fissionable material that can sustain a chain reaction

(physics) the mass of a body as measured when the body is at rest relative to an observer, an inherent property of the body

(physics) the mass of a body in motion relative to the observer: it is equal to the rest mass multiplied by a factor that is greater than 1 and that increases as the magnitude of the velocity increases