Real Dictionary

fluff
Fluff consists of soft threads or fibres in the form of small, light balls or lumps. For example, you can refer to the fur of a small animal as fluff.
verb: If you fluff something that you are trying to do, you are unsuccessful or you do it badly.
verb: If you fluff things such as cushions or feathers, you get a lot of air into them, for example by shaking or brushing them, in order to make them seem larger and lighter.

fluff in American English
soft, light down
to become fluffy
to shake or pat until loose, feathery, and fluffy
intransitive verb: to become fluffy; move, float, or settle down like fluff
noun: light, downy particles, as of cotton
transitive verb: to make into fluff; shake or puff out (feathers, hair, etc.) into a fluffy mass

fluff in British English
noun: soft light particles, such as the down or nap of cotton or wool
verb: to make or become soft and puffy by shaking or patting; puff up