Stacks, or piles, refer to a collection of items arranged in a vertical manner, typically with one item placed on top of another. This organization allows for efficient use of space and easy access to the items. Common examples of stacks include books on a shelf, plates in a cupboard, or boxes in a storage area. In computer science, a stack is a data structure that follows the Last In, First Out (LIFO) principle. This means that the most recently added item is the first one to be removed. Stacks are used in various applications, such as managing function calls in programming and undo mechanisms in software.