Definition:
Shared services from an organisation perspective is the consolidation of business operations that are used by multiple parts of the same organisation. Shared services are cost-effiecient as they are centralised back-office operations that are used by multiple devisions of the same company and eliminate redundancy.
Shared services refers to a dedicated unit of people, processes or technologies that is structured as a centralised point of service and is focused on defined business functions. SAFe framework utilises these specialist roles, people and services that are necessary for the success of agile release train (ART) or Solution train which cannot be dedicated full-time. These specialised resources are quite busy so there must be a plan to engage shared services whenever needed.
Utilising shared services saves time and improves productivity by eliminating the need for individual development teams, provides cost savings with a volume agreement, decreases legal fees with a multi-year agreements, allows organisation to obtain economies of scale, drives efficiency throughout the organisation providing high-quality applications to development teams, accelerates speed to market of quality software products.
Further Reading:
https://en.wikipedia.org/wiki/Shared_services
https://searchcio.techtarget.com/definition/Shared-services
https://www.scaledagileframework.com/shared-services/
https://www.gartner.com/it-glossary/shared-services