recovery.conf is a simple configuration file placed in the top level of the data directory which is used with standby servers to specify the location of the primary server for streaming replication, or when starting up a server using archived WAL files, or performing PITR.
As a file for configuring streaming replication, its name is somewhat counterintuitive, but makes sense from the historical development of PostgreSQL's replication methods. It might be an idea to think of streaming replication standbys as "permanently in recovery".
Note that in contrast to other directly editable configuration files,
recovery.conf cannot be relocated outside of the data directory.
If a standby is promoted,
recovery.conf is renamed to
recovery.conf file is included in the source code at src/backend/access/transam/recovery.conf.sample, though it does not contain all possible parameters.