What is the primary operation performed on a stack data structure?

The primary operation performed on a stack data structure is the combination of 'push' and 'pop' operations. A stack follows a Last In, First Out (LIFO) principle, meaning that the most recently added element is the first one to be removed.

The 'push' operation is used to add an item to the top of the stack, while the 'pop' operation removes the item from the top of the stack. These two operations are fundamental to how stacks function and are crucial for managing data in a way that supports the LIFO order. Stacks are commonly used in various applications, such as function call management in programming and undo mechanisms in software applications, precisely because they can easily manage and access data in this manner.

In contrast, the other options focus on isolated actions (insert, retrieve, and sort) that do not fully encapsulate the unique operational behavior of stacks. For instance, while insertion and retrieval can occur in many data structures, only the push and pop operations can be directly associated with stack behavior.