Backup system that's partially running and can take over quickly but not instantly. Like having a car engine that's warmed up but not fully running.
E-commerce sites use warm standby systems that can activate within minutes, balancing cost and recovery speed.
Warm standby is a disaster recovery pattern (not a single product) where a scaled-down but functional environment is kept running in a secondary site/region and can be scaled up during failover. AWS Elastic Disaster Recovery, Azure Site Recovery, Google Cloud Backup and DR, and OCI Full Stack Disaster Recovery can replicate workloads and orchestrate recovery to support warm-standby-style designs, typically combined with autoscaling and DNS/traffic failover.