An eating disorder is a complex compulsion to eat in a way which disturbs physical, mental, and psychological health. The eating may be excessive (compulsive over-eating); to limited (restricting); may include normal eating punctuated with episodes of purging; may include cycles of binging and purging; or may encompass the ingesting of non-foods. The most commonly heard about eating disorders are Anorexia nervosa and Bulimia nervosa. The most widely and rapidly spreading eating disorder is compulsive overeating or Binge eating disorder. These are also the three most common eating disorders. All three have severe consequences to a person's immediate and long-term health and can cause death. There are numerous theories as to the causes and mechanisms leading to eating disorders

More Info, Source and Links:
http://en.wikipedia.org/wiki/Eating_disorder