Dirt Wall is a background wall made from Dirt Blocks. A naturally occurring variety of Dirt Walls are generated with a new world, as the background in most caves and under most overhangs above 0 depth (above the Underground layer). They will not stop enemies from spawning and are not suitable for housing. In addition, they drop nothing when destroyed with a Hammer.
Non-naturally occurring Dirt Walls can be recognized by their slightly different sprite (they have tiny grey stones, where natural ones are plain dirt but have occasional large rocks). Additionally, they function properly for housing, and drop items when broken. They blend with the generated walls.