Also called: recovery point objective, acceptable data loss
In plain English
RPO is the maximum amount of data you can afford to lose in a disaster, expressed as a time window ("at most 30 seconds"). In an asynchronous PostgreSQL setup your real RPO is simply the replication lag at the instant of failure — the WAL the disaster site hadn’t received yet.
Why it matters
It’s a measurable number, not a slogan: you can read it as the byte gap between the primary’s current WAL position and the standby’s received position. Monitoring that gap is how you keep your actual RPO inside your target.