Acceleration - if the velocity of an object incerases with time in the direction of the motion of the object,then the acceleration of the body is known as positive acceleration.
deceleration - if the velocity of an object decreases with time ,then the acceleration of the object is known as deceleration.                             
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Acceleration= rate of change of velocity is know as accelration

Decelration=Deceleration is the opposite of acceleration.   When you decelerate, your                       velocity decreases over time. 
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