Villa is a generic term, and one not always used by Disney.
The DVC Vacation Homes come in several different formats. A studio: two beds and a small kitchenette with mini refrigerator, microwave, coffee maker, or one bed and a pull out couch. A one bedroom vacation home: king bed in a separate bedroom, large bathroom with jacuzzi tub, separate laundry room/closet, full kitchen with all appliances and dishes, cutlery ect. Some of the newer one bedrooms have two bathrooms (AKLV and BLTV).
Two bedrooms add a second bedroom, with two beds, and another bathroom. A Grand Villa adds enough sleeping accommodation for fourteen people. They are often two storey and very nice.
Off site the term is used generically to mean a condo or a fully self contained house that people rent (usually by the week) for their stay.
A hotel room is usually a bathroom one or two beds, and a closet with no cooking options, although Disney does not for most hotel rooms have the small fridge.