Wiktionary
n. (context physics English) the mass of a body when it is not moving relative to an observer
WordNet
n. (physics) the mass of a body as measured when the body is at rest relative to an observer, an inherent property of the body
Usage examples of "rest mass".
He and I have disagreed about the quantization of quasar red shifts, the explanation of superluminal light sources, the rest mass of the neutrino, quark physics in neutron stars.
Some time ago, the ship's momentum exceeded half its rest mass, at which point a single kilogram packs the punch of a multimegaton hydrogen bomb.
The closer a ship in normal space crowded c, the speed of light, the more relativistic mass it possessed, and the more energy per kilogram of rest mass it took to accelerate it .
That figure is almost twice the actual rest mass in the neighborhood.
Since quanta have no rest mass, the pulsations disturbed the geometry of space according to the laws of Einsteinian mechanics.
Add just one more nine after the decimal point and you have a ship that weighs seventy times its rest mass.
But if the rest mass is zero it does not matter how many times you multiply it.
Our best intelligence gives it a maximum tau factor of point two and a dry rest mass of three kilotons—.
That means that the colony ships won't convert to rest mass when they reach the receiver.