Accession
The process by which an archives takes legal and physical custody of records, formally bringing them into its holdings — and the body of records so transferred.
Accession refers both to the act of an archives formally taking custody of records and to the group of records transferred in a single such action. When permanent records reach the end of their active life, they are transferred to an archives, which accessions them — accepting legal and (for physical records) physical custody, recording their receipt, and bringing them under archival control.
In the U.S. federal government, permanently valuable records are accessioned by the National Archives, which then becomes responsible for preserving them and making them available. Accessioning is distinct from transfer (the movement of the records) in that it denotes the receiving institution’s formal acceptance of responsibility.