Step 1: Understand what a stack is. A stack is a data structure that follows the Last In, First Out (LIFO) principle.
Step 2: Learn the basic operations of a stack. The main operations are 'push' (to add an item), 'pop' (to remove the top item), and 'peek' (to view the top item without removing it).
Step 3: Identify what a queue is. A queue is a different data structure that follows the First In, First Out (FIFO) principle.
Step 4: Know the operations of a queue. The main operations of a queue are 'enqueue' (to add an item) and 'dequeue' (to remove the front item).
Step 5: Compare the operations of stacks and queues. Notice that 'dequeue' is an operation specific to queues and is not allowed in stacks.
Step 6: Conclude that 'dequeue' is the operation that is not allowed in a stack.
