Prefab is related to prefabricated construction. The word "Prefab" is not an industry term like modular homes, manufactured homes, panelized home, or site-built home. The term is an amalgamation of panelized 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.