Longman Dictionary of Contemporary English
Wiktionary
n. A type of house which shares both sidewalls with the adjacent houses, typical of Victorian and Edwardian housing in English cities.
WordNet
n. a house that is part of a terrace
Wikipedia
A terraced or terrace house ( UK) or townhouse ( US) is a term in architecture and city planning referring to a style of medium-density housing that originated in Europe in the 16th century, where a row of identical or mirror-image houses share side walls. They are also known in some areas as row houses or linked houses.
Terrace housing can be found throughout the world, though it is in abundance in Europe and Latin America, and extensive examples can be found in Northern America and Australia. The Place des Vosges in Paris (1605–1612) is one of the early examples of the style. Sometimes associated with the working class, historical and reproduction terraces have increasingly become part of the process of gentrification in certain inner-city areas.