There’s a couple of ways to look at what the jerk settings do. From a dead stop, the jerk setting defines the first move rate the firmware will factor into the move planning, and it will accelerate from that rate as required. When already moving and about to make a change in speed or direction, the jerk setting defines the instantaneous step the firmware can make in the feed rate.

Visualize this on a motor vehicle. For the smoothest ride, you put the vehicle in gear and slowly let out the clutch and give it some gas to gradually accelerate from a stop. To corner nice and smooth, you slow down to a near stop to complete the turn and then gradually accelerate back up to the speed limit. All this takes time. If you’re in a hurry, you can drop the vehicle into gear without using the clutch and the vehicle will lurch forward. To save more time, you can screech around the corners almost to the point the vehicle goes out of control. Completing the turn, you might need to adjust the steering for a while to get the vehicle moving in a straight line again. In a similar way, the jerk settings allow you to set where in the range you want the printer to run – slow and conservative, or fast and bouncy. (Referenced from http://3dprintboard.com)