Unusual elements of a motion picture created using a variety of techniques such as computer, mechanical, makeup, pyrotechnic, optical, lighting, camera speed, weather effects, and model techniques. Generally they are used to create effects that normal camera techniques or set action cannot provide or would be too costly to shoot normally. They are often inserted into the motion picture by the special effects department after live shooting.

Source: Art & Architecture Thesaurus

http://vocab.getty.edu/page/aat/300263877