Also called: promotion, promote signal, pg_ctl promote
In plain English
pg_promote() is the PostgreSQL function that tells a standby to stop following the primary, exit recovery, and become a primary in its own right. Promotion ends replay, opens the database for writes, and advances the timeline so future WAL is distinguishable from the old primary’s.
Why it matters
This is the actual verb behind every failover and switchover — whether you run it manually or a cluster manager like Patroni calls it for you. The timeline bump it triggers is what lets the rest of the cluster (and pg_rewind) tell the new history apart from the old.