noun
Clumps of fabric fibers, often found on clothing or in dryers.
セーターに綿ぼこりがたくさんついている。
There's a lot of fluff on the sweater.
noun
dustball; ball of dust
A small, roundish accumulation of dust and fibers, often found under furniture.
Dustballs had collected under the bed.
ほこり is general dust, while 綿ぼこり specifically refers to fibrous fluff or dustballs.
Compound of 綿 (cotton, fibers) and ほこり (dust).