So what exactly is considered a factory or manufactured house?

I live in a century old American Foursquare that was originally ordered out of a Sears catolog. It was picked out of a catolog ca. 1907, shipped to our town via rail, and then assembled on site based on instructions. In fact, while up in the attic or down in the crawl space, you can still see some of the original part numbers on the various exposed timbers.

Yeah, it's not exactly a trailer or a modern prefab, but I'm sure if Sears was capable of transporting an entire house at the turn of the century, they would have...