Mach’s name was not coined as a term until 13 years after his death in 1916. A Swiss engineer named the variable after Ernst Mach in a 1929 paper to honor the Austrian’s work on the understanding of supersonic flow.
Mach is perhaps most well-known in the aviation community, and in particular the aviation community that flies very fast jets. A Mach number is a dimensionless number that represents the speed of an object moving through a fluid (most commonly air), divided by the speed of sound in that fluid. Mach 1.0 represents the speed of sound in any given fluid.