Final answer:
The range of virtual addresses assigned by z/OS is known as an address space, a concept that is crucial for virtual memory management and task isolation within the system.
Step-by-step explanation:
The range of virtual addresses that z/OS can assign to a user or separately running program is called a(n) address space. The z/OS operating system manages these address spaces, which are unique for each task or job in the system. Virtual memory allows the operating system to provide an application the illusion of a large, contiguous block of memory, which is abstracted from the actual physical memory available. The concept of address spaces allows for isolation and protection of the memory regions allocated to different tasks, ensuring that they do not interfere with each other.