The set of policies and procedures used to restore critical systems after a catastrophic event. Defined by two key metrics: RPO (how much data you can afford to lose) and RTO (how long you can afford to be down).
In AZ-900: Azure Site Recovery. In CLF-C02: AWS Backup, pilot light, warm standby. It is a major topic in SAA-C03. Typical question: the difference between RTO and RPO, and which services reduce each one.
Disaster recovery (DR) is a concept that can show up on the exam. Check the full guide to see it in context.