Massive particle
（重定向自Tardyon）
The term massive particle refers to particles which have real non-zero rest mass. According to special relativity, their velocity is always lower than the speed of light. The synonyms bradyon (from Greek:βραδύς, bradys, “slow”), tardyon or ittyon are sometimes used to contrast with luxon (which moves at light speed) and hypothetical tachyon (which moves faster than light).