The time derivative of acceleration is called the jerk. As you might guess, it describes the rate that acceleration is changing. It is often considered important in cam-follower system design.
I moved your thread to the corresponding technical forum, as the introduction forum is only meant in case you want to tell us something about yourself.
The answer to your question is it represents the magnitude of the rate of change of acceleration, i.e. whether you accelerate slowly or have a kick-start.