PostgreSQL kill – Sighup pid [closed]

To reload the configuration files, we send the SIGHUP signal to the
postmaster, which then passes that on to all connected backends.
That’s why some people call reloading the server “sigh-up-ing”.

As reloading the configuration file is achieved by sending the SIGHUP
signal, we can reload the configuration file just for a single
backend using the kill command.

First, find out the pid of the backend using pg_stat_activity. Then,
from the OS prompt, issue the following:

kill  -SIGHUP pid

I dont understand bold words. Because we have many PIDs for backend and if we kill a PID, how can it get changes from reload configuration file (postgresql.conf)?