**Retardation**

Retardation is the act or result of delaying; the extent to which anything is retarded or delayed; that which retards or delays.

**Difference between Retardation and Acceleration**

Acceleration and retardation both are just the rate of change of velocity of a body/particle. As velocity and 'rate of change of velocity' are vectors we can differentiate them on the basis of the direction of 'rate of change of velocity' w.r.t the direction of velocity. If the direction of both the 'rate of change of velocity' and velocity are same then the 'rate of change of velocity' is called acceleration. If the direction of 'rate of change of velocity' and velocity are opposite to each other then the 'rate of change of velocity' is called retardation.