Accession refers to the process of gaining or acquiring something, often in a formal or official manner. In a legal context, it can involve the addition of new rights or properties to an existing estate or collection. For example, when a country joins an international organization, it is said to have achieved accession to that group. In the context of libraries and archives, accession describes the process of receiving and cataloging new materials, such as books or documents. This ensures that the items are properly recorded and made accessible for future use, maintaining the integrity of the collection over time.