A Burrow is a naturally occuring object that randomly spawns in Grassland Biomes in the Reign of Giants. Moleworm will spawn at Dusk and Night from Burrows and start roaming around the area looking for minerals to store inside it. Burrows can be dug up with a Shovel to randomly get Rocks, Flint, Nitre and Gold Nuggets. When dug, Burrows will also drop any item stole by Moleworms as long as there weren't more than 50 of them.
If a Burrow is dug up, the Moleworm that inhabited it will make a new one after some time, making them renewable.