A bayonet is the currently most widely used type of lens mount.
Bayonet mounts are all based on the same principle: you insert the lens into the camera’s mount rotated away from its proper setting, then twist the lens (around the optical axis) until it is properly oriented, at which time it locks. Most lens mounts (e.g. Canon EF, Sony FE) are mounted clockwise (when looking at the camera from the front), but some (e.g. Nikon F) are mounted counterclockwise.
The unlocking mechanism is typically based on a button or a lever which withdraws the bayonet mechanism’s locking pin, and that button or lever is typically on the camera, beside the mount. In some cases, the unlocking mechanism is also on the lens itself (e.g. Olympus OM).
Other types of lens mounts:
- thread/screw mounts
- breech-lock mounts