A cloud-based backup service for VMs, databases, files, and on-premises workloads. Backups are stored in Recovery Services Vaults.
Configured for VMs and databases in AZ-104. AZ-900 mentions it as the backup solution for disaster recovery. Question: what Azure service do you use to back up VMs? Azure Backup.
Azure Backup is a concept that can show up on the exam. Check the full guide to see it in context.