Final answer:
RACF (Resource Access Control Facility) is the system that allows organizations to define individuals and groups with access privileges to IBM's z/OS. It is an essential element for maintaining the security of the operating system by controlling who can access specific resources.
Step-by-step explanation:
The system that enables an organization to define individuals and groups with access privileges to z/OS is RACF (Resource Access Control Facility). RACF is a security feature that provides access control and auditing functionality for the z/OS operating system. It allows administrators to define users and groups, and to specify the types of access that are allowed to various resources, such as datasets, files, and transactions. RACF ensures that only authorized personnel can access sensitive data, thus helping to protect the system from unauthorized use. Other options like APF (Authorized Program Facility), JES (Job Entry Subsystem), and SVC (Supervisor Call) serve different purposes within the z/OS environment.