filter bed
nounUK /ˈfɪltə bɛd/ · US /ˈfɪltɚ ˌbɛd/
1
A layer of gravel, sand, or other material through which liquid is passed in order to remove impurities; also, a pond or tank containing such a layer.
Entry derived from the Wiktionary, under licence CC BY-SA 4.0 — list of authors.