Backup retention is the length of time backup copies are kept before they are deleted or overwritten. It is a core part of backup policy because a backup that exists only briefly may not be available when a team needs to recover from accidental deletion, ransomware, failed updates, or account loss.
In cyber security, retention matters because attackers often try to destroy recovery options after compromising a system. Long enough retention can give defenders time to detect an intrusion, isolate affected systems, and restore clean data. Too-short retention can leave an organization with no usable historical copy, while too-long retention can increase storage cost and exposure of sensitive data. Good practice is to define retention based on recovery needs, legal requirements, and restore testing, so backups are not just created but still recoverable when it counts.