Speed is the rate of distance covered per unit of time. The SI unit for speed is meters per second. An object can have a speed of any number 0 or greater.
Speed is a scalar measurement, meaning the direction of movement of an object cannot be determined by just knowing the speed. Velocity is a vector measurement that indicates the speed and direction of movement. The speed of an object is easily measured using a radar gun, using a laser gun, or simply recording the time taken to move a known distance. The speedometer of a car determines the current speed by recording the revolution rate of the tires divided by a set time interval.