International Association of Home Safety and Security Professionals define locks as:

"A device that incorporates a bolt, cam, shackle or switch to secure an object - such as a door, drawer or machine - to a closed, opened, locked, off or on position, and that provides a restricted means of releasing the object from that position."

Types of locks based on installation method

Rim Lock: designed to be mounted on the surface or rim of a door or object.

Mortise Lock: installed in a hollowed out or mortised cavity.

Bored or Bored-in Lock: installed by cross-boring two holes - one for cylinder and one for the bolt mechanism.

Types of locks based on internal construction

Warded Lock: A ward is a fixed projection designed to obstruct unauthorized keys from entering or operating the lock. Provides little security as wards are easy to bypass with a stiff piece of wire or thin strip of metal.

Tumbler Lock: Tumblers are small objects, usually made of metal that move within a block cylinder in ways that obstruct a lock's operation until an authorized key or combination moves them into alignment. Provides more security that a ward lock. Different type of tumbler locks are: Lever Tumbler Locks, Disc Tumbler Locks and Pin Tumbler Locks.

Reference: Phillips, Bill; The Complete Book of Locks and Locksmithing, fifth edition, McGraw Hill, 2001

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