A bolt is the portion of a lock located in the doorjamb that is inserted into a door in order to secure it. A dead bolt (or dead lock) is the term for a type of locking mechanism that requires that the lock cylinder be decidedly rotated — with a key or latch — to move the bolt to the open position. Conversely, the more common, less secure spring bolt lock simply uses a spring to hold the bolt in place, allowing movement of the bolt by turning the doorknob or lever. The two types of locking mechanisms — dead bolt and spring bolt lock — are commonly used together for enhanced security and maximum flexibility.
See also: bolt