Techopedia explains ClientThe SAP client concept allows an organization to split a system into logical subunits. Clients may operate as separate business units, where all data is stored in a common database. Access rights for each client are defined during the installation process. Client specific data includes user master data (including authorizations and user groups), data customization and application/business data.The number of clients in a SAP system directly influences the following:Buffer: The number of clients impacts buffering demand. An example is main memory usage.Upgrade: Different activities are affected by SAP upgrades, where run timers are longer, depending on the number of clients.SAP also defines clients with the following roles, as required in a complete landscape.Client CUST: Used for making developments and serving other customer-specific requirements. The SAP transport management system is used to move CUST client changes to other clients.Client QST: Defined for testing and verifying various applied changes.Client PRD: Used for production and business activities.