Fluff?

[Hive]

I know fluff means the back stories of the wh40k universe but what does it actually stand for? :)

[Cailet]

It isn't an acronym if that's what you're thinking, it's just the backstory.

[Volsung]

I have no idea where it came from, it just is a word that means all the character, history, and other backstory of Warhammer 40,000 and it's universe :)

[Skullbreak]

People call the backstory "fluff" because (I believe), back when the game was relatively new, they thought of the background as relatively unimportant and as an excuse for armies to fight. Fluff can refer to anything of little consequence, so players adopted the name.