A jerk is a sharp, sudden movement. When you're learning to drive a stick shift, it’s hard to avoid the jerk and lurch when you try to change gears. Jerk is also a very unflattering term for an obnoxious person.
Although you will most commonly hear the derogatory jerk as in "Don't be such a jerk," there are many other meanings of the word. ""Clean and jerk" is an Olympic weightlifting event where you lift a barbell in one "clean" movement, then, in one quick thrust — the jerk — you lift the weight above your head. Jerk can also mean making a sharp, sudden move — like a dog jerks on his chain. You may have eaten jerk, also called jerky — strips of dried meat — handy for lunchboxes and camping.