Question

What does rate of change rate of change of acceleration mean?

Answer 1

Rate of change of anything is the change in that quantity divided by time taken for this change.
So, rate of change of acceleration is the change in acceleration by the time in which the acceleration changes.

Example, Let a car be tarvelling with acceleartion 2m/s^2. After 10 seconds, let its acceleration be 6m/s^2.
So, rate of change in acceleration is 6-2/10=3/10=0.3m/s^2

Please understand that, this is rarely used, as rate of change of acceleration is not as important as rate of change of displacement( velocity) or rate of change of velocity(acceleration).

In physics, rate of change of acceleration is called jerk.