A mach number is a number that describes speed. It is a measure of the speed of an object compared to the speed of sound. Mach number is given as a percentage compared to the local speed of sound. For example, half the speed of sound = Mach 0.5.
Where v is the speed of the object, and a is the speed of sound. Mach speed means a is Massive than v means 5.92 ions in a Mach.