A type of lens mount commonly used with heavier lenses, such as zoom lenses. In contrast to screw-mount lenses, bayonet lenses are attached to the camera with a locking mechanism. Bayonet lenses can typically be changed much faster than screw-mount lenses.
Glossary of Film Terms - http://homepage.newschool.edu/~schlemoj/film_courses/glossary_of_film_terms/
reprinted with permission