A landfill is a site for waste disposal by burial.
Non-toxic waste material from landfills were often used as replicator material by a variety of species, like the Romulans and the Hydrans, with the latter worshipping a god dedicated specifically for landfills, the God of Landfills. (RIS Bouteina: "If At First You Don't Succeed")
Lyrans operated landfills on Class B planets, as well as Class C planets, to dispose of radioactive or otherwise dangerous waste. (Star Trek: The Stoneship Files: "Cruchitude Dump")