Gurney -

In the US, anything that can be hooked up and unhooked to be dragged behind a tow vehicle is generally called a trailer. It's a very generic term that includes things towed by bicycles, motorcycles, tractors (farm and highway=semi-tractor), automobiles, trucks, and anything else they can be hooked up to. The key is that they can be unhooked.

Most trailers have wheels, but the term is used for special purpose things with skis (snow) or rarely skids (for mud). In general, anything that can be dragged behind and can be separated from what drags it. The only exception I can think of is that the term is seldom applied things towed behind a boat, where more specific terms are usually used (other boat, skier, idiot, fool ... etc)

A Google Image Search shows a fairly general variety of "US Trailers" although they mixed in a few clinkers.

(I'm not sure whether the hot(?) chick pulling a suitcase with wheels quite qualifies, but she's walking past a bigger trailer (trailer house?) in the background so that might be what they meant.)

The link does show a number of "campers/camping trailers" that have been mentioned in the thread.

John