This article is from the Diet FAQ, by Claudia McCreary email@example.com with numerous contributions by others.
Physicians usually define "overweight" as a condition in which a person's
weight is 10-20% higher than "normal", as defined by a standard
height/weight chart. "Obesity" is usually defined as a condition in which a
person's weight is 20% or more above normal weight. "Morbid obesity"
variously means 50% to 100% over normal weight, more than 100 pounds over
normal weight, or sufficiently overweight to severely interfere with health
or normal functioning.