What Does Flexible Single-Master Operation Mean?
Flexible single master operation (FSMO) is a Microsoft Active Directory feature that is a specialized domain controller task used when standard data transfer and update methods are inadequate. Tasks that do not suit multimaster replication are only viable as flexible single-master operations.
Multimaster models have a number of operators, which are held by a single master. This problem is solved by applying a number of operations to a single domain controller. A single domain controller holds the role for a particular operation and is the single master for that operation. These operation masters are called flexible single-master operations.