Speed. (not velocity)

The speed would be slow and if it was fast.

rate of change of displacement is known as velocity it shows that how fast or slow a body is moving and in which direction it is moving.

To change the acceleration of a car: speed up, slow down or turn.

Acceleration is any change in velocity.

Velocity is "how fast" and in "what direction".

To speed up is to accelerate (increase the velocity).

To slow down is to deaccelerate (decrease the velocity)

To turn is also a form of acceleration (changes the direction of the velocity).

not a fast but slow