As we talked about the stack in previous pages, we already know that stack is a linear data structure with the LIFO principle. As a result, stacks have only one end to add a new item or remove an item. It is one of the oldest and most used data structures in computer technology. We always add or remove an item from a stack using the single point named top. The term push is used to indicate an item to be added on top of the stack and pop to remove an item from the top; this is shown in the following diagram. We will discuss more about stacks in Chapter 4, Constructing Stacks and Queues.