Wiki article on this topic: A townhouse, townhome, or town house as used in North America, Asia, Australia, South Africa and parts of Europe, is a type of terraced housing. A modern town house is often one with a small footprint on multiple floors. In British usage, the term originally referred to the city residence of someone whose main or largest residence was a country house.
Historically, a townhouse was the city residence of a noble or wealthy family, who would own one or more country houses in which they lived for much of the year. From the 18th century, landowners and their servants would move to a townhouse during the social season.
In the United Kingdom, most townhouses are terraced. Only a small minority of them, generally the largest, were detached, but even aristocrats whose country houses had grounds of hundreds or thousands of acres often lived in terraced houses in town. For example, the Duke of Norfolk owned Arundel Castle in the country, while his London house, Norfolk House, was a terraced house in St James's Square over 100 feet wide.
In the United States and Canada, a townhouse has two connotations. The older predates the automobile and denotes a house on a small footprint in a city, but because of its multiple floors , it has a large living space, often with servants' quarters. The small footprint of the townhouse allows it to be within walking or mass-transit distance of business and industrial areas of the city, yet luxurious enough for wealthy residents of the city.
Townhouses are expensive where detached single-family houses are uncommon, such as in New York City, Chicago, Boston, Philadelphia, Toronto, Washington, DC, and San Francisco.
Rowhouses are similar and consist of several adjacent, uniform units originally found in older, pre-automobile urban areas such as Baltimore, Charleston , Savannah and New Orleans, but now found in lower-cost housing developments in suburbs as well. A townhouse is where there is a continuous roof and foundation, and a single wall divides adjacent townhouses, but some have a double wall with inches-wide air space in between on a common foundation. A rowhouse will generally be smaller and less luxurious than a dwelling called a townhouse.