A dirt road or dirt track is an unpaved road not paved with asphalt, concrete, brick, or stone, made from the native material of the land surface through which it passes, known to highway engineers as subgrade material. Unpaved roads with a harder surface made by the addition of material such as gravel and aggregate (stones) might be referred to as dirt roads in common usage, but are distinguished as improved roads by highway engineers. Improved unpaved roads include gravel roads and macadamized roads.

Source: Wikipedia