A light-proof housing for x-ray film, containing front and back intensifying screens, between which the film is placed and held during exposure. Although it is usual to have two screens, there may be only one where there is a special need for a high detail picture.
Cassettes are also used in Computed Radiography (CR) Systems but holding an Imaging Plate (IP) instead of film. In this case we will refer to this as the cassette or cassette shell.
See “Imaging Plate” and “Computed Radiography”