Real Dictionary

stack
countable noun: A stack of things is a pile of them.
plural noun: If you say that someone has stacks of something, you mean that they have a lot of it.
verb: If someone in authority stacks an organization or body, they fill it with their own supporters so that the decisions it makes will be the ones they want it to make.
verb: If you stack a number of things, you arrange them in neat piles.

stack in American English
a large pile of straw, hay, etc., esp. one neatly arranged, as in a conical form, for outdoor storage
to pile or arrange in a stack
noun: a more or less orderly pile or heap

stack in British English
to place in a stack; pile
noun: an ordered pile or heap

stack in Chemical Engineering
noun: A stack is a very tall chimney used for getting rid of waste gases.