A terrace, terraced house (UK), or townhouse (US) is a type of medium-density housing which 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.

Terrace housing can be found worldwide, though it is quite common in Europe and Latin America, and many examples can be found in the United Kingdom, Belgium, United States, Canada, and Australia. The Place des Vosges in Paris (1605–1612) is one of the early examples of the type.

Although in early larger forms it was and still is used for housing the wealthy, as cities and the demands for ever smaller close housing grew, it regularly became associated with the working class. Terraced housing has increasingly become associated with gentrification in certain inner-city areas, drawing the attention of city planning.

Though earlier Gothic examples, such as Vicars' Close, Wells, are known, the alignment of the house fronts with the property line really began in the 16th century following Dutch and Belgian models and became called "row" houses in English. For example, in "Yarmouth Rows", Great Yarmouth, Norfolk, the building fronts all were right on the property line.

The term terrace was borrowed from garden terraces by British architects of the late Georgian period to describe streets of houses whose uniform fronts and uniform height created a stylish ensemble rather than a mere "row" of similar homes. Townhouses (or townhomes) are generally two- to three-story structures that share a wall with a neighbouring unit. As opposed to apartment buildings, townhouses do not have neighbouring units above or below them. They are similar in concept to row houses or terraced houses, but share a common design and construction. The first and last of the houses is called an end terrace and is often a different layout from the houses in the middle, sometimes called mid-terrace.

In Australia, the term "terrace house" refers almost exclusively to Victorian and Edwardian era terraces or replicas almost always found in the older, inner city areas of the major cities. Terraced housing was introduced to Australia from Britain in the nineteenth century, basing their architecture on those in the UK, France and Italy.

Large numbers of terraced houses were built in the inner suburbs of large Australian cities, particularly Sydney and Melbourne, mainly between the 1850s and the 1890s (terraced housing is rare outside of these cities). Detached housing became the popular style of housing in Australia following Federation in 1901. The most common building material used was brick, often covered with cement render and then painted.

Many terraces were built in the "filigree" style, a style distinguished through heavy use of cast iron ornament, particularly on the balconies and sometimes depicting native Australian flora. In the 1950s, many urban renewal programmes were aimed at eradicating them entirely in favour of modern development.