Books are arranged in the library according to their subject. Because it would be impossible to describe the subject in words on the spine of each book, libraries use codes for these subjects. These codes are called "call numbers," and the system of call numbers is called a "classification scheme."
Some libraries (especially public libraries) use the Dewey Decimal classification scheme. At HCC Library (as in many academic libraries, WCU, ASU, ABTech, etc.) we use the Library of Congress Classification scheme, or LoC for short. For detailed information about LoC classes and subclasses, see the Library of Congress Classification Outline.