Final answer:
In computing, 'locality' refers to the principle where a set of pages that are actively used together during program execution, demonstrating a pattern of memory access. This concept includes types such as temporal and spatial locality, fundamental for caching and memory allocation.
Step-by-step explanation:
The correct answer to the question “A locality is” would be a) a set of pages that are actively used together. The term ‘locality’ in computing refers to the principle of locality, which is a pattern of computer program execution where the same memory locations are frequently accessed during a short period of time. This idea is crucial in the design of modern caching and memory management. There are two types of locality: temporal locality, where the same resources are reused within a relatively small time frame, and spatial locality, where nearby locations to the recently accessed memory are likely to be accessed soon.