Also called: async replication
In plain English
Asynchronous replication means the primary commits and returns to the client without waiting for any standby to confirm it received the WAL. The standby catches up a moment later. It’s the default and the only practical choice across long (cross-region) network distances.
Why it matters
It keeps commit latency low by not paying a network round-trip per transaction — but it means a small, bounded window of recent commits can be lost if the primary dies before the standby receives them. That window is your RPO.