dust bunny

noun1

1. •
   (US, informal) A small clump of dust, fluff, hair, particles of skin, etc., that tends to accumulate indoors in areas not regularly dusted, such as under heavy furniture.

   • Phobos just can't catch a break. Not only is Mars' lumpy, crusted-over dust bunny of a moon destined to be ripped to pieces in 10 million years, it seems the poor thing can't stop punching itself. — 2016