Mach Number

The ratio of true airspeed to the speed of sound in the same atmospheric conditions; e.g., MACH .82, MACH 1.6. Named in honor of Ernst Mach, late 19th century physicist.

Source: 14 CFR Federal Aviation Regulations §1, Pilot Contoller Glossary (PCG), Pilot Handbook of Aeronatical Knowledge

See also:

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