Answer:
A massless particle is an elementary particle whose invariant mass is zero.
Explanation:
An elementary particle or fundamental particle is a subatomic particle with no substructure, i.e. it is not composed of other particles.
The invariant mass, rest mass, intrinsic mass, proper mass, or in the case of bound systems simply mass, is the portion of the total mass of an object or system of objects that is independent of the overall motion of the system.
