Keyed alike cylinders
If several cylinders (on the picture all cylinders) are locked with only one key (S.1), we are speaking about keyed alike cylinders (the all cylinders have the same inner code). The number of keys (in the example key S.1) does not matter.
This locking solution is not yet called a locking system.
In this example you can see several keyed alike cylinders. These all are lockable by only one key. The keys work completely independently of each other.
There is only one key for each keyed alike cylinder.
The respective number of keys (in the example S.1, S.2, S.3 and S.4 ) plays no role.