MARCOS, or the MARC (Machine-Readable Cataloging) format, is a standard for the representation and communication of bibliographic and related information in machine-readable form. It is widely used in libraries and information centers to facilitate the sharing and exchange of cataloging data. MARC records contain fields that describe various aspects of a resource, such as its title, author, publication date, and subject matter. The MARC format has evolved over the years, with different versions like MARC21 being commonly used today. It allows libraries to create, manage, and share their collections efficiently, supporting interoperability between different library systems and enhancing access to information for users.