Architecture where one system actively handles traffic while backup systems wait on standby. Like having a backup quarterback ready to enter the game if needed.
Enterprise databases often run active-passive mode with one primary database serving requests while replicas stay ready for failover.
Active-passive is an architecture pattern, not a single cloud service. All major clouds support it using combinations of load balancers, health checks, DNS failover, multi-zone/region deployments, and database replication/failover features.