Kilometer per hour is a measure of speed, typically used in countries that use the metric system. In these countries, road speed limits are calculated in kilometers per hour, which is abbreviated as kph or km/h. As its name implies, this unit represents the distance (in kilometers) traveled by an object for one hour. This measure is usually an average, that is, if a car traveled the distance of 210 km between two cities and to take this route, it took an hour and a half, so we will get a speed of 140 kilometers per hour (140 km/h). This does not obviously mean that the car has constantly shifted at this speed, there may be parts of the route on which it has been faster and parts where it has circulated more slowly.
Mach is a velocity measure defined as the ratio of an object's velocity to the speed of sound. In other words, the Mach speed corresponds to the number of times an object has reached the speed of sound. The speed of sound is not constant and depends on the medium where the sound is propagated. In the Earth's atmosphere, if we take into account a temperature of approximately 15 degrees Celsius, the speed of sound is 1225 km/h. This is the reference measure used by the Mach speed, and thus, Mach 1 corresponds to exactly that value. The air force has combat aircraft with speeds several times higher than the speed of sound, they are the so-called supersonic planes. Most of them can fly at a speed equal to or greater than Mach 4, that is, four times the speed of sound. There are already some projects for the construction of airplanes that can reach the surprising speed of Mach 20.