Obesity is a medical term which describes a condition where excess body fat has accumulated to the extent that it may have an adverse effect on health, leading to reduced life expectancy and/or increased health problems.
One definition of "fat" is a layman's term for obesity.
The terms fat or thin should be no more derogatory than tall or short, having brown hair or blonde hair. They are just descriptions which should be neutral regarding desirability. Yet we are brainwashed into believing some body types are more desirable than others. Desirability is a personal preference, not a universal standard.
Perceived desirability is influenced by cultural and personal tastes. Many cultures and individuals find obesity attractive or desirable. Obesity can be perceived as a sign of wealth and affluence. However in western culture, we've become obsessed with being thin... in the case of super models, the current standard is near anorexic and unhealthy IMO. Personally, I find the body shape of most super models unattractive. They are too thin according to my personal tastes. I find women with a curvy solid athletic build desirable like these women athletes:
Then theres....