Definitions:

1. A number representing the ratio of the speed of a body, such as an aircraft, to the speed of sound in a surrounding medium, such as air. NOUN
   • At Mach 1, the aircraft's speed equaled the speed of sound, creating a distinct shock wave.
2. Named after Austrian physicist Ernst Mach, is a critical parameter in aerodynamics and aeronautics for describing the speed of an aircraft, missile, and other projectiles relative to the speed of sound in the air around them. NOUN
   • The Mach number is a critical factor in aerodynamics, affecting aircraft performance, drag, and fuel efficiency.

Synonyms:

• aerodynamic speed
• flight mach number
• flow speed
• sonic speed
• speed ratio
• velocity ratio