A prefabricated structure or building is a structure that has several factory built components that are assembled on a site. These pre-made components can consist of panels, modules or transportable sections

The word "Prefab" is not an industry term like modular home, manufactured home, panellized home, or site-built home. The term is an amalgamation of panellized and modular building systems, and can mean either one. In today's usage the term "Prefab" is more closely related to the style of home, usually modernist, rather than to a particular method of home construction.

Buildings have been built in one place and reassembled in another throughout history. Possibly the first advertised prefab house was the Manning Portable Cottage. A London carpenter, Henry Manning, constructed a house that was built in components, then shipped and assembled by British emigrants. This was published at the time (advertisement, South Australian Record, 1837) and a few still stand in Australia. One such is the “Friends Meeting House, Adelaide”. The peak year for the importation of portable buildings to Australia was 1853, when several hundred arrived. These have been identified as coming from Liverpool, Boston and Singapore (with Chinese instructions for re-assembly). In Barbados the Chattel house was a form of prefabricated building which was developed by emancipated slaves who had limited rights to build upon land they did not own. As the buildings were moveable they were legally regarded as chattels.