Velocity is change of position with time. Velocity can be calculated at an instant (you look down and your speedometer says you are traveling 100 km/hr, or it might be calculated as an average (we traveled 160 km in 2 hrs, our average velocity was 80 km/hr).
Velocity appears in the Kinematic Equations.
The study of velocity and related topics led to the development of Calculus. A technique in calculus, called Integration, uses a function of Velocity vs. Time to calculate distance traveled (also called Displacement). Another technique in calculus, called Differentiation, uses a function of Velocity vs. Time to calculate Acceleration.
Vectoreverything 