120: What is 120 or medium format film?
120 or medium format film is so called because it is larger than 35mm or 135 format film, but smaller than 4×5 sheet film, which is called large format.
120 film usually comes wrapped around a plastic spool, and yields 12 or 16 images, depending on which camera and film masks you use. The terms “120 film” and “medium format film” are pretty much interchangeable nowadays, but it is important to know that the film is not 120mm.
Medium format film does require a bit of special care in that it must be processed and printed at a professional photo lab – most drugstore or one-hour labs will not be able to process 120 film of any kind.