Some libraries have closed stacks which are not open to the public, but most libraries allow their users to browse all or part of their stack areas. Stacks can either be closed (not directly accessible by users) or open. The open stacks movement revolutionized the purpose and role of libraries.
The word choice of "stacks" over "shelves" in libraries can cause user frustrations amongst those not familiar with the term; "Where are the stacks?" can be a common question at the reference desk.
See also: Naming conventions