Acceleration is a rate in which the velocity is changing. Acceleration is also a rate and it measures how the velocity is changing with respect to time. 
     When the driver in an automobile presses  the gas pedal it usually goes faster and thats what we call acceleration. Whenever we are changing our state of motion, we are accelerating.
     Another term for acceleration is the decrease or increase of speed. It also applis to changes in direction and changes in speed.
     EXAMPLE: A car that can go from 0 to 60 km/h in 5 seconds has a  greater acceleration than another car that can go from 0 to 80 km/h in 10 seconds.
     So having good acceleration means being able to change velocity quickly. It doesnt always mean how fast something is moving.