Bradyon

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A tardyon or bradyon is a particle that travels slower than light. Therefore this is a synonym with a massive particle (i.e. a particle having a non-zero mass). This includes all known particles (except luxons). The term "tardyon" is constructed to contrast with "tachyon", which refers to hypothetical particles that travel faster than light. Tardyons cannot break the light-speed barrier.

Tardyons have real masses, whereas luxons have zero (both real and imaginary) mass. Tachyons have an imaginary mass

The words "tardyon" and "bradyon" are neologisms and are not yet in wide use, even within the field of physics.