What term is used to compare the speed of a moving body to the speed of sound?

The term used to compare the speed of a moving body to the speed of sound is "Mach." This term is derived from the name of the Austrian physicist Ernst Mach, who conducted early studies on the properties of sound and supersonic motion. When an object moves at the speed of sound, it is said to be traveling at "Mach 1." Speeds greater than the speed of sound are classified as supersonic (Mach greater than 1), while speeds less than the speed of sound are subsonic (Mach less than 1). This terminology is pivotal in aerospace and aviation, particularly when discussing aircraft performance and the dynamics of flight at various speeds. The other terms relate to different concepts within physics and aviation; for instance, velocity refers to the speed of an object in a specified direction, knots measure speed typically used in maritime and aviation contexts, and thrust refers to the force that propels an aircraft forward.