Data Facility Storage Management Subsystem (MVS)
Data Facility Storage Management Subsystem (DFSMS) is a central component of IBM's flagship operating system z/OS. It includes access methods, utilities and program management functions. Data Facility Storage Management Subsystem is also a collective name for a collection of several products, all but two of which are included in the DFSMS/MVS product.
Source: Wikipedia — Data Facility Storage Management Subsystem (MVS) (CC BY-SA 4.0)