the fluff that gets stuck in your belly button, usually yellow or blue,.. rarely red but is possible.. if you don't clean it out with a cotton bud, it stinks!and turns black and gets sticky

1) strange fabric that is found in the belly button.
2) nickname for someone who puts his finger in his belly button.
3) old skin that is inside your belly button

someone who collects belly button fluff is called: a belly button fluffer