When fats aggregate into body and weight suddenly increase continuously it is called obesity. Obesity is the name of extra fat in the body according to medically point of view. if you want to check obesity there are many situations to diagnose obesity.
Like if skin fold in men more then 30MM it is obesity, and if in women it is more then 23MM it is also called obesity.
Medically obesity can be check by measuring some fixed units like Age Gender and height, width if any unit increases in body it is known as obesity. There are many of forms and similar words that can be use as alternative of obesity like
corpulence adipose obesity adiposity are some keywords that mostly used to describe obesity.