A lock cylinder refers to the part of a lock where you insert the key. It is a cylindrical tube-shaped component that contains various mechanisms inside, like pins and springs, which allow the lock to function properly. Full definition
When the engine continues running after turning off the ignition switch, it typically is due to a failure of the ignition switch, ignition relay or the ignition lock cylinder. (yourmechanic.com)
Replacement Door Lock Cylinder Kit is a high quality product to replace your old or damaged factory unit. (carparts.com)
At the rear of the vehicle insert the vehicle key in the rear compartment lock cylinder located in the lower left and cycle the key 5 times within 5 seconds. (mechanics.stackexchange.com)