Flab is the soft, loose flesh on a person’s body — the kind that hangs or moves, not tight muscle. People use this word when they do not like that flesh; it carries a little scorn. You hear it in talk about diets and gyms (“lose the flab”). It is informal. A doctor would not write flab on a chart. Though actually, almost everybody has some, and the word makes it sound uglier than it is. You can also hear it used a little loosely for any extra weight someone wants to lose.

贅肉