Prefab is short for “prefabricated,” which means “made beforehand,” and not “before fabulous.” Prefab things are made in sections that can be easily shipped and put together to form a finished product. Some buildings and houses are prefab.
Prefab can be used as a noun or adjective. When you talk about a cool prefab you saw downtown, you mean a prefabricated building, one that was built from parts that were shipped and quickly assembled. Prefab shelters have been made from converted shipping containers. Some furniture is sold this way, too, like a prefab bookshelf in flat box that contain sections you can take home and put together easily. Or so say the directions.