Obesity means a condition in which a person has too much body fat. It is different from being overweight, which means weighing too much since weight may come from muscle, bone, fat and/or body water. However, both terms mean that a person's weight is greater than what is considered healthy for his or her height. Although obesity is an individual clinical condition, it is increasingly viewed as a serious and growing public health problem: excessive body weight has been shown to predispose to various diseases, particularly cardiovascular diseases, diabetes mellitus type 2, sleep apnea and osteoarthritis. The goal of obesity treatment is to achieve and maintain a healthier weight.

See also: http://en.wikipedia.org/wiki/Obesity