What does "rest mass" mean?

The mass of a body when it is not moving relative to an observer.

What is a synonym for "rest mass"?

Common synonyms include: intrinsic mass, invariant, invariant mass, proper mass.

noun

noun ·Rare ·Advanced level

Noun

1
The mass of a body when it is not moving relative to an observer.
2
(physics) the mass of a body as measured when the body is at rest relative to an observer, an inherent property of the body wordnet