(n.) 1. 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.
Source: Phillips, Bill; The Complete Book of Locks and Locksmithing, fifth edition, McGraw Hill, 2001
(n.) 2. The part in a lock that releases the bolt when moved by a key.
Source: Dictionary.com