Circulation is a library term that means checking out library materials to users. It is used to designate the service desk where you check out and return materials, as well as the library staff that work at those desks

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"Circulating books" are books that can be checked out. They are shelved in the main shelving area of the library, often called the "stacks". Circulating books cover all subject areas and can range from broad overviews of a general topic to very detailed studies of a very limited, specific topic.