A disaster recovery strategy where a scaled-down but fully functional version of the entire environment is always running in the DR region. When a disaster hits, you only need to scale up capacity, not start components from scratch.
In SAP-C02 it offers an RTO of 1-5 minutes and an RPO of seconds, at a higher cost than Pilot Light because it keeps compute running permanently. Route 53 with health checks is used to direct traffic to the DR region and scale the Auto Scaling Group.
DR Strategy: Warm Standby is a concept that can show up on the exam. Check the full guide to see it in context.