Locking is the means to avoid concurrent modifications to an Object by restricting access to the entity (often a Client but could also be an internal process) that initiated the lock. LockingServices are typically used to make a set of changes (for example, several Write operations and Method invocations) and where a consistent state is available only after all of these changes have been performed.
The context of the lock is specific to the ObjectType where it is applied to (subsequently named "lock-owner"). These specifics need to be described as part of this lock-owner ObjectType. See for example the section on lock in the TopologyElement (clause 4.3) and the Network (clause 5.3).
By default, a lock allows other Applications to view (navigate/read) the locked element. However, Servers may choose to implement an exclusive locking where other Applications have no access at all (e.g. in cases where even read operations require certain settings to Variables).