Revolutions
This is the number of revolutions (or turns) that it will take to wind up the spring so that it is tightly wrapped around the drive axle. It is also the number of revolutions that the axle will go through when the spring is allowed to unwind. Therefore, it determines how many times the drive wheels will rotate when the car is allowed to go forward.
The number of revolutions is determined by many things, including the length of the spring, the diameter of the drive axle, the thickness of the spring, and the inner diameter of the spring case.