Final answer:
In some formal languages, stored data that the system accesses and alters is called a data structure.
Step-by-step explanation:
The correct term for stored data that the system accesses and alters in some formal languages is Data structure. A data structure is a way of organizing and storing data in a computer, so that it can be efficiently accessed, modified, and used. Examples of data structures include arrays, linked lists, stacks, and queues.