AACR2, or the "Anglo-American Cataloguing Rules, Second Edition," is a set of guidelines used for cataloging library materials. It was first published in 1978 and aimed to standardize the way libraries organize and describe their collections. This helps ensure that users can easily find and access information. The rules cover various types of materials, including books, journals, and audiovisual items. AACR2 emphasizes the importance of providing clear and consistent bibliographic information, which is essential for effective library management and user navigation. It has since been succeeded by RDA, or "Resource Description and Access," which builds on its principles.