Wood is a natural material hewn from tree trunks, which is inexpensive and readily available in many places. It is often used as a facade material for agricultural and residential buildings.

The wood forms the exterior surface rather than necessarily the load-bearing frame. A building can therefore have a wood facade over a supporting structure of another material.

Bark is the tree's outer covering and has a separate facade-material identity. Wood concerns the material hewn from the trunk beneath that covering.