rest mass

noun, Physics.

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

Compare relativistic mass.

Origin

1910-15

British Dictionary definitions for rest mass

rest mass

noun

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

rest mass in Medicine

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

rest mass in Science

rest mass
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.