A terrace, terraced house (UK), or townhouse (US) is a kind of medium-density housing that first started in 16th century Europe with a row of joined houses sharing side walls. In the United States and Canada these are sometimes known as row houses or row homes.

Medium-density housing is a term used within urban planning and academic literature to refer to a category of residential development that falls between detached suburban housing and large multi-story buildings. There is no singular definition of medium-density housing as its precise definition tends to vary between jurisdiction. Scholars however, have found that medium density housing ranges from about 25 to 80 dwellings per hectare, although most commonly sits around 30 and 40 dwellings/hectare. Typical examples of medium-density housing include duplexes, triplexes, townhouses, row homes, detached homes with garden suites, and walk-up apartment buildings.