General

Obviously, the differences between plump, chubby, and fat are according to the observer. What is your perspective?

"Plump" and "chubby" mean the same thing. In fact, the definition of the word "chubby" is "plump and rounded."

"Chubby" and "fat" are very distinct. Chubby refers to being soft and overweight. Fat refers to being obese. Of course, there are people who call anyone that isn't slim and trim "fat". I suppose that's technically true in the sense they have an excess of fat on them. But these days, I don't think anyone would call someone who is built, thick, or curvy "fat" due to the ratio of muscle to fat.

At 5-11 and 205, I’d qualify as being bit round in the middle, At 5-3 and 320 and growing, my other half qualities as being fat and comfortably obese. Pretty clear there :-)