A break period used to go masturbate because you're aroused or your mind is preoccupied with sex. Typical among males. Jerk breaks are usually taken during periods of light physical activity and intense brain activity such as studying for a midterm, writing an essay, reading a book for your book report, filling out tedious income tax forms, or what have you.
Jerk breaks are cathartic in many ways.
Man I've been reading this same fucking page for fifteen minutes and I've got a big boner and can't concentrate. I think this calls for a jerk break. JERK BREAK!