Switchover
Also called: planned failover, controlled role reversal
A switchover is a planned, controlled reversal of roles: the current primary steps down cleanly and a standby is promoted, with no data loss because everything is in sync first. It contrasts with a failover, which is the unplanned, emergency version after the primary has already failed.
What this means
A planned, tidy swap of roles: the current primary steps down cleanly and a standby takes over, with zero data loss because everything is in sync before the switch. It's the calm, scheduled cousin of a failover, the same idea, but done in a hurry after the primary has already crashed.
Why it matters operationally
Switchovers are how you do zero-downtime-ish maintenance (patching, region moves) and, crucially, how you rehearse your DR plan: a planned switchover exercises the whole RTO path safely. Afterwards the old primary can rejoin with pg_rewind.