Stacks or stack area refer to the space in a library where the majority of library materials are shelved. There are 3 floors of "stacks" in the East Wing and 7 floors of "stacks" in the West (Bing) Wing. Green Library also has other locations so make sure your catalog record says the book is in STACKS.
Here is a map (not to scale) of the stack areas . Here is a Stack Directory by Call number. You can access this from your Mobile Phone  too! (we also have pocket Stack Location Guides at the Information Center desk).