Libraries use classification systems to organize the books on the shelves. A classification system uses letters and/or numbers (Call Numbers) to arrange the books so that books on the same topic are together. This arrangement can result in serendipitous browsing, where you find one book in the catalog, go to the shelf, and, an even better book is sitting right next to it.
The Library of Congress (LC) system is broken into 21 primary classes, or general subject areas, represented by letters.
The Ort Library uses Library of Congress (LC) call numbers for most of its collection.
You might be familiar with the Dewey Decimal Classification System from high school or the public library. Most colleges and universities use the Library of Congress (LC) Classification System because it accommodates larger collections and facilitates academic research.
The Library of Congress Classification System is subject-based, classifying and arranging items by the subject matter involved.
This video is from Ryerson University Library and Archive and explains how to read a call number.
This is another video, from the University of Arkansas Library, which explains how to read a call number.