allow me to answer that for you
In the case of an object moving through a fluid, such as an aircraft in flight, the Mach number is equal to the velocity of the object relative to the fluid divided by the velocity of sound in that fluid.
Displacement is a vector quantity, which means that we need to specify a magnitude and direction. So, unlike distance, displacement cares what direction the object is going when it moves between two points. So, in one dimension, displacement can be positive, negative, or zero
