A daemon is a process running in the background. In NuttX a daemon process is a task, in POSIX (Linux / Mac OS) a daemon is a thread.
New daemons are created through the
daemon_task = px4_task_spawn_cmd("commander", SCHED_DEFAULT, SCHED_PRIORITY_DEFAULT + 40, 3600, commander_thread_main, (char * const *)&argv);
The arguments here are: