Final answer:
Velocity is defined as the speed of an object in a specific direction, a vector quantity that includes both magnitude (speed) and direction. The SI unit for velocity is m/s.
Step-by-step explanation:
The best definition of velocity is that it is the speed of an object in a specific direction. Velocity is a vector quantity, which means it includes both a magnitude (how fast the object moves) and a direction. For instance, saying something is moving at 20 kilometers per hour south illustrates its velocity because it shows both the speed and the direction of movement.
The SI unit for velocity is m/s. Instantaneous velocity is defined as the velocity of an object at a specific instant in time, essentially the average velocity for an infinitesimally small interval. By contrast, average velocity is calculated as the displacement divided by the total time taken for that displacement.