What is Lock ?
Lock is (noun) 1. an object which closes a door or closes a container such as a box, so that you can only open it with a key She left the key in the lock, so the burglars got in easily. We changed the locks on the doors after a set of keys were stolen. under lock and key locked up firmly We keep our jewels safely under lock and key. 2. an amount by which the wheels of a car can turn left or right The car has an excellent lock – it turns easily in a narrow road. 3. a section of a canal or river with gates which can be opened or closed to control the flow of water, and so allow boats to move up or down to different levels They passed through dozens of locks on their trip down the Thames. 4. lock, stock and barrel everything all together (verb) 1. to close a door or a container such as a box, so that you need to use a key to open it I forgot to lock the safe. We always lock the front door before we go to bed. 2. to fix or to become fixed in a certain position The wheels suddenly locked as he went round the corner.
source: Easier English, Student Dictionary Upper Intermediate Level