euphemism for a chubby person. not a morbidly obese person but a person who is generally more voluminous than the expected norm. for women it also means curvy or voluptuous.
tom: that fat girl in accounting just told me to bug off.
steve: she isn't fat, she's fluffeh.
The Luftwaffe pilots would line up, drop their pants, and let the uniformed men of the Flufferwaffe jack them off and suck their dicks before flying into air combat.