Fluff in Britain means small, loose bits of material such as lint or down.
In Britain fluff can also mean other things in slang such as making a mistake, something unimportant and even a sexual partner.
"A bit of fluff" can refer to a casual sexual partner, especially one that is considered attractive but not serious.
This is a less common usage of the term fluff in Britain and other places and is also considered to be offense by many people.
"A bit of fluff" in Britain and other places can also be a derogatory term for something that is considered insignificant or superficial and is also often used to describe women and is a more dated usage and is often considered to be offense today.
And "to fluff" in Britain and other places can also mean to make a mistake, and most particularly in performance.
For example, an actor may "fluff their lines" during a play.
This is a common usage in both American English and British English.
Fluff in Britain also refers to small and light and loose bits of material like fuzz, downy fibers or even lint.
For example you may find some fluff on your clothes or in a dryer lint trap.