A person who, while they have very low weight on the scales, and may look reasonably (or even very) skinny with heavy clothes on, they still have a large amount of body fat compared to muscle, resulting in a flabby appearance. Hence, a skinny (low mass) person, who still looks fat (flabby and untoned).
Often, vegetarians who have no idea where to get non-meat protein-rich foods from, and don't know why it's important, so they end up having no muscle. Especially vegetarian girls which combine the above with eating like a rabbit to "lose weight".
This is your average teenage (or not so teenage) girl who has been misled by hollywood to think that any form of exercise that isn't jogging will make you look like Arnold Schwarzennegger. Usually involves this vicious cycle:
a) "OMG! I look fat!"
b) "I need to eat like a rabbit from now on to lose weight" (myth)
c) "I need to go running every morning to increase my tone" (myth)
d) "I should avoid any other form of exercise because I will bulk up and look ugly instead" (super-myth - in fact it's the opposite)
e) Result: Loss of weight, but more muscle than fat lost, resulting in more fat remaining relative to body muscle (i.e. looking even more flabby and lumpy than before)
f) OMG! I look fat! --> back to a). Also, welcome to the anorexia club.
"How can I look so fat! I weigh no more than my 10-year-old!"
"You're just skinny-fat. You need some more muscle, and then you'll look drop-dead gorgeous again. Stop jogging and starving yourself, and go do some more wholesome exercise instead."