noun - Numbers that are written in black on the shoulders, upper arms, shoulder blades, thighs, calves, wrists and/or swim caps of the swimmers for identification purposes prior to the start of the race. These numbers are used to monitor the swimmer’s progress, announ - ce the swimmer’s position to the crowd and media, and to inform swimmers who commit rule infractions during the race. Paddlers, kayakers and escort boats for individual swimmers can also be marked on both sides with the swimmer's race number so it is easily seen from both sides. The race officials write markings on the swimmer’s shoulders 30 minutes before the start of the race. Synonyms: race numbers and competitor’s numbers.