A mobile home (in the United States; also called a trailer or trailer house) or a static caravan (in other countries; also called a caravan) is a prefabricated home built in a factory, rather than on site, and then taken to the place where it will be occupied. Being built on a permanently attached chassis with highway-grade wheels and tires, mobile homes are usually transported by being pulled behind a tractor-trailer over public roads to a home site. Mobile homes share the same historic origins as travel trailers, but today the two are very different in size and furnishings, with travel trailers being used primarily as temporary or vacation homes.
 
Mobile homes are usually placed in one location and left there permanently, but they do retain the ability to be moved, as required in many areas. Behind the cosmetic work fitted at installation to hide the base, there are strong trailer frames, axles, wheels, and tow-hitches.
 
Mobile homes come in two major sizes, single-wides and double-wides. Single-wides are 18 feet (5.5 m) or less in width and 90 feet (27 m) or less in length and can be towed to their site as a single unit. Double-wides are twenty feet 20 feet (6.1 m) or more wide and are 90 feet (27 m) in length or less and are towed to their site in two separate units, which are then joined together. Triple-wides and even homes with four, five, or more units are also built, although not as commonly.
 
While site-built homes are rarely moved, single-wide owners often "trade" or sell their home to a dealer in the form of the reduction of the purchase of a new home. These "used" homes are either re-sold to new owners or to park owners who use them as inexpensive rental units. Single-wides are more likely to be traded than double-wides because removing them from the site is easier. In fact, only about 5% of all double-wides will ever be moved.