What does 55mm camera mean?

The question likely pertains to 55mm as a lens focal length, and does not relate to any type of camera.

Another use for numbers like 55mm in connection with a lens is to designate the thread size of the filters and lens caps that lenses require. For the interchangeable lenses used on 35mm SLR cameras, those sizes commonly run from 49mm to 72mm. Cameras are designated by film size or by type. Some common camera designations are 35mm; SLR; rangefinder; digital; point-and-shoot; medium format; view camera; press camera (various types); TLR twin lens reflex) -- there are others. If there is a "55mm"camera, I haven't encountered it.