Operations Support Systems (OSS), or Operational Support Systems in British usage, are computer systems used by telecommunications service providers to manage their networks (e.g., telephone networks). They support management functions such as network inventory, service provisioning, network configuration and fault management.
Together with Business Support Systems (BSS), they are used to support various end-to-end telecommunication services. BSS and OSS have their own data and service responsibilities. The two systems together are often abbreviated OSS/BSS, BSS/OSS or simply B/OSS.
The acronym OSS is also used in a singular form to refer to all the Operations Support Systems viewed as a whole system.
Different subdivisions of OSS have been proposed by the TM Forum, industrial research labs, or OSS vendors. In general, an OSS covers at least the following five functions:

Network management systems
Service delivery
Service fulfillment, including the network inventory, activation and provisioning
Service assurance
Customer care