Mud

From DwarfFortressWiki

Indoor mud is created by filling a stone floor tile with water, then letting the water evaporate. Outdoor mud is created by covering any soil tile with water. Creating mud is essential to providing irrigation for subterranean crops, as well as any crops indoors. The most common sources for mud are the results of irrigation, farming, and draining water sources.

Building a construction, such as a dirt road, over muddy tiles will remove the mud.

In adventurer mode mud objects which you can pick up from muddy tiles are edible.^{v0.27.176.38c}