In architecture and city planning, a terrace or terraced house (UK) or townhouse (US)[a] is a form of medium-density housing that originated in Europe in the 16th century, whereby a row of attached dwellings share side walls. They are also known in some areas as row houses or row homes (especially in locations such as Philadelphia, New York, Baltimore, Boston, Washington, D.C., Chicago, Pittsburgh, and St. Louis).

A house is a single-unit residential building, which may range in complexity from a rudimentary hut to a complex structure of wood, masonry, concrete or other material, outfitted with plumbing, electrical, and heating, ventilation, and air conditioning systems. Houses use a range of different roofing systems to keep precipitation such as rain from getting into the dwelling space. Houses may have doors or locks to secure the dwelling space and protect its inhabitants and contents from burglars or other trespassers.