rest mass

noun Physics.

1. the mass of a body as measured when the body is at rest relative to an observer, an inherent property of the body.

noun

1. the mass of an object that is at rest relative to an observer. It is the mass used in Newtonian mechanics

n.

1. The physical mass of a body when it is regarded as being at rest.

1. In Special and General Relativity, the observed mass of a body that is not in motion with respect to the observer. Also called invariant mass Compare relativistic mass.