Daemon (computer software)
From Wikipedia,

“In Unix and other computer multitasking operating systems, a daemon is a computer program that runs in the background, rather than under the direct control of a user; they are usually initiated as background processes.

Systems often start (or “launch”) daemons at boot time: they often serve the function of responding to network requests, hardware activity, or other programs by performing some task. Daemons can also configure hardware (like devfsd on some Linux systems), run scheduled tasks (like cron), and perform a variety of other tasks.”

At least on the open source side we can see what software processes are running. Microsoft has that “secret” OS that we can not be sure of what it is doing.