In Japan, the Semi format (セミ判) is the 4.5×6cm format, giving 16 exposures on 120 film. The word "Semi" (セミ) often appears in the names of older Japanese 4.5×6 cameras. Most of these are folders: see the page about the Japanese 4.5×6 folders. There is also a handful of models with a rigid body and a telescopic lens, made in the late 1930s and early 1940s.
The word Semi was abandoned for camera names in the 1950s, together with the disappearance of the 4.5×6 models. The format was revived in 1975 with the Mamiya M645, and the term "645" has since been used in many camera names, like the Fujica GS645 and GW645, Pentax 645, Contax 645 and Bronica RF645.