1. [n]  a storage device that handles data so that the next item to be retrieved is the item most recently stored (LIFO)
2. [n]  a large tall chimney through which combustion gases and smoke can be evacuated
3. [n]  a list in which the next item to be removed is the item most recently stored (LIFO)
4. [n]  an orderly pile
5. [n]  (often followed by `of') a large number or amount or extent; "a batch of letters"; "a deal of trouble"; "a lot of money"; "he made a mint on the stock market"; "it must have cost plenty"
6. [v]  arrange in stacks; "heap firewood around the fireplace"; "stack your books up on the shelves"
7. [v]  load or cover with stacks; "stack a truck with boxes"
8. [v]  to arrange in a stack or pile; "stagger the chairs in the lecture hall"

1. \Stack\, a. [Icel. stakkr; akin to Sw. stack, Dan. stak.
   Sf. {Stake}.]
   1. A large pile of hay, grain, straw, or the like, usually of
      a nearly conical form, but sometimes rectangular or
      oblong, contracted at the top to a point or ridge, and
      sometimes covered with thatch.
            But corn was housed, and beans were in the stack.
                                                  --Cowper.
   2. A pile of poles or wood, indefinite in quantity.
            Against every pillar was a stack of billets above a
            man's height.                         --Bacon.
   3. A pile of wood containing 108 cubic feet. [Eng.]
   4. (Arch.)
      (a) A number of flues embodied in one structure, rising
          above the roof. Hence:
      (b) Any single insulated and prominent structure, or
          upright pipe, which affords a conduit for smoke; as,
          the brick smokestack of a factory; the smokestack of a
          steam vessel.
   {Stack of arms} (Mil.), a number of muskets or rifles set up
      together, with the bayonets crossing one another, forming
      a sort of conical self-supporting pile.
   

2. \Stack\, v. t. [imp. & p. p. {Stacked}; p. pr. & vb. n.
   {Stacking}.] [Cf. Sw. stacka, Dan. stakke. See {Stack}, n.]
   To lay in a conical or other pile; to make into a large pile;
   as, to stack hay, cornstalks, or grain; to stack or place
   wood.
   {To stack arms} (Mil.), to set up a number of muskets or
      rifles together, with the bayonets crossing one another,
      and forming a sort of conical pile.
   

(See below for synonyms) A data structure for storing items which are to be accessed in last-in first-out order.

The operations on a stack are to create a new stack, to "push" a new item onto the top of a stack and to "pop" the top item off. Error conditions are raised by attempts to pop an empty stack or to push an item onto a stack which has no room for further items (because of its implementation).

Most processors include support for stacks in their instruction set architectures. Perhaps the most common use of stacks is to store subroutine arguments and return addresses. This is usually supported at the machine code level either directly by "jump to subroutine" and "return from subroutine" instructions or by auto-increment and auto-decrement addressing modes, or both. These allow a contiguous area of memory to be set aside for use as a stack and use either a special-purpose register or a general purpose register, chosen by the user, as a stack pointer.

The use of a stack allows subroutines to be recursive since each call can have its own calling context, represented by a stack frame or activation record. There are many other uses. The programming language Forth uses a data stack in place of variables when possible.

Although a stack may be considered an object by users, implementations of the object and its access details differ. For example, a stack may be either ascending (top of stack is at highest address) or descending. It may also be "full" (the stack pointer points at the top of stack) or "empty" (the stack pointer points just past the top of stack, where the next element would be pushed). The full/empty terminology is used in the Acorn Risc Machine and possibly elsewhere.

In a list-based or functional language, a stack might be implemented as a linked list where a new stack is an empty list, push adds a new element to the head of the list and pop splits the list into its head (the popped element) and tail (the stack in its modified form).

At MIT, pdl used to be a more common synonym for stack, and this may still be true. Knuth ("The Art of Computer Programming", second edition, vol. 1, p. 236) says:

  Many people who realised the importance of stacks and queues
  independently have given other names to these structures:
  stacks have been called push-down lists, reversion storages,
  cellars, dumps, nesting stores, piles, last-in first-out
  ("LIFO") lists, and even yo-yo lists!

[Jargon File]