Force in the direction of the objects motion = Acceleration
Force in a direction other than that of the objects motion = Deceleration
Explanation:
Force - a push or a pull that is applied on an object.
Motion - change in position of an object.
When force is applied in the direction of the moving object, it is called as Acceleration.
When force is applied in the opposite direction of the moving object, it is called as Deceleration.
