invariant mass
Technical term in physics; also called rest mass. Used in special relativity and particle physics.
The invariant mass is invariant under Lorentz transformations.
静止質量 (rest mass) is often used interchangeably with 不変質量, but 不変質量 emphasizes the invariance under Lorentz transformations.
Compound of 不変 (invariant) and 質量 (mass), a direct translation of the English term 'invariant mass'.