For questions generally relating to the structure and construction of floors in buildings, including designs, materials, support mechanisms, load-bearing calculations, etc. For questions specifically about the top-layer covering of a floor (tile, carpet, hardwood) see the "flooring" tag.
A floor is the walking surface of a room or vehicle. Floors vary from simple dirt in a cave to many-layered surfaces using modern technology. Floors may be stone, wood, bamboo, metal, or any other material that can hold a person's weight.
The levels of a building are often referred to as floors although a more proper term is storey.
Floors typically consist of a subfloor for support and a floor covering used to give a good walking surface. In modern buildings the subfloor often has electrical wiring, plumbing, and other services built in. Because floors meet many needs, some essential to safety, floors are built to strict building codes in the first world.
In light-frame residential construction, floors are constructed in two basic designs; either as part of a concrete slab foundation (which includes the floor of a basement or the first floor of "slab-on-grade" construction) or by using a series of horizontal timbers called joists, which are anchored to load-bearing walls and/or support columns, and then covered with plywood or other sheathing to provide a stable continuous surface for a floor covering.
Related tag: flooring - for questions specifically relating to top-level floor coverings, such as hardwood, carpet, or tile.