what is eating disorder?

well,eating disorders are abnormal eating habits that may involve either inadequate or excessive food intake to the detriment of an individual's physical and mental health.In other words, eating disorders are more than just going on a diet to lose weight or trying to exercise every day. They're extremes in eating behavior — the diet that never ends and gradually gets more restrictive, for example. 

source: http://kidshealth.org/teen/food_fitness/problems/eat_disorder.html