A buyer’s guide
Three questions answer it for most homes. Each type carries a different label, and the label is what lenders, zoning offices and buyers go by.

A HUD manufactured home has a red and silver metal label on the outside of each section it was shipped in. It sits at the end where the taillights were during transport, about a foot up from the floor and about a foot in from the side. A double-wide has two. If you find one, the home was built to the federal HUD code. It also has a paper data plate inside, usually near the electrical panel, in a bedroom closet or inside a kitchen cabinet.
A modular home is built to the building code of the state it was delivered to and carries that state's label instead of a HUD label. Look on or inside the electrical panel door, under the kitchen sink, or in a utility closet.
A park model RV is built to the ANSI A119.5 recreational vehicle standard, is limited to 400 square feet, and sits on a single chassis. It usually has an RVIA seal near the entry door and is usually titled as an RV, not as real estate.
The home is probably site-built or a kit. Your county's building permit records will show how it was approved.
Labels get painted over, covered by skirting or pulled off. Your state's manufactured housing agency can look up the records. For a HUD home, IBTS, the organization that keeps the HUD label records, can issue a letter confirming the label numbers for a fee. If a house sold as modular has a HUD label, the HUD label decides it: the home is a manufactured home. A home built before June 15, 1976 predates the HUD code and will not have a HUD label at all.
The type decides which lots and zones allow the home, whether it can get a regular mortgage or only a chattel loan, and how appraisers value it at resale. Modular homes are usually financed and appraised like site-built houses. HUD homes on land with a permanent foundation can qualify for a mortgage. Park models are usually financed like RVs.