Ok, i will come to terms with the idea that neither "prefab" and the word it abbreviates, "prefabricated" have been noded yet. Something prefab has been assembled (or mostly assembled) before purchase, and is pretty much explicitly associated with modern (industrial and post-) consumerism. Prefab smacks of artificiality, as prefab things are inescapably manufactured, as opposed to organic in any way. Prefab items are generally ready to use, right out of the box (so to speak); prefab homes became popular when the suburban aesthetic came in and are still, if not popular, common in economically depressed areas, where they are a step up from mobile homes (also prefab, actually). You can get log-cabin-style prefab houses, or ranch style (unlike the dressing, more like the ticky tacky).

Prefab also becomes a metaphor for something which could be built by hand or developed organically, but is produced by an industry to suit a market: see the Monkees' nickname The Prefab Four. Like so many bubblegum pop bands, they were assembled by players in the industry (in this instance, the music industry) in order to compete in the market exemplified by the Beatles' popularity. People who fall into stereotypes, especially ones common in media, could be said to have prefab personalities. You get the idea. It's more or less pejorative, these days. But it is really cool to see big sections of prefab houses rolling down the highways on Wide Load trailers.