The connection service file allows libpq connection parameters to be associated with a single service name. That service name can then be specified by a libpq connection, and the associated settings will be used. This allows connection parameters to be modified without requiring a recompile of the libpq application. The service name can also be specified using the PGSERVICE environment variable.
To use this feature, copy share/pg_service.conf.sample to etc/pg_service.conf and edit the file to add service names and parameters. This file can be used for client-only installs too. The file's location can also be specified by the PGSYSCONFDIR environment variable.