In a nutshell, it's the shell: Everything that separates and protects indoors from out-including exterior walls, insulation, roofing, foundation and flooring, windows, and doors.
This is among the more unpleasant byproducts of households and industrial processes: It's waste material that can pose a threat to human health or the environment if handled improperly. According to the Environmental Protection Agency (EPA), waste is hazardous if it has at least one of four qualities: ignitability, corrosivity, reactivity, or toxicity.