What is retardation?

negative accelereation is called retardation 

If the velocity of an object decreases with time and its direction is opposite to the direction of velocity, then that motion is called retardation / deceleration / negative acceleration.

Hope this helps

Retardation is the actually negative acceleration. It can be defined as the rate of decrease of velocity.

Example: The acceleration of the car is -5 Km/hr = The retardation of the car is 5 Km/hr

if the velocity of an object decreases with time and its direction is opposite to the direction of velocity, then that motion is called retardation / deceleration / negative acceleration

v-t graph shows the retardation.

Retardation is the actually negative acceleration. It can be defined as the rate of decrease of velocity.

Example: The acceleration of the car is -5 Km/hr = The retardation of the car is 5 Km/hr

  Retardation is the application of a force that produces negative accelleration. Synonyms would be braking, decelleration, damping, etc. Gravitational force operates downward (in a negative direction) so, in most frames of reference, gravity is a retarding force.

If  the  velocity  of  an  object  decreases  in  the  same  direction,  the  object  has  a  negative  acceleration.  It  is  called  decceleration  or  retardation.

thanks people :D

Dude I will explain u Practically,

Now what happens that take a motorcycle or bicycle and after paddling for 5 sec than stop paddling now it's velocity or accelaration do not become 0 as it is than also moving for some time, than the accelaration become Retardation.