A triplex is a building divided into three separate homes — three apartments in one house, each with its own door, kitchen and bathroom. It sits in a family of American property words: a duplex has two homes, a triplex three, a fourplex four. This is mainly North American English; in Britain people would describe the same building as 'a house converted into three flats', and in Taiwan you will meet the word mostly on English-language rental sites and in American films. Watch out for one confusing point: in some places, especially American estate agents' listings, 'triplex' is also used for a single home spread over three floors — so the word can mean either 'three homes in one building' or 'one home on three levels', and only the rest of the sentence tells you which. As an adjective, triplex simply means threefold or having three parts, but that use is technical and rare. Triplex is also a well-known brand of safety glass, which is why you may see the word on a car windscreen.

三戶住宅、三聯式住宅（一棟樓分成三戶；美式用法，台灣較常說「三戶一棟」或直接講「三層樓的房子」— 但注意英文有時指「一戶三層樓」）