Pronounced "dee-mun" as in the word for devil, as well as "day-mun," a daemon is a Unix/Linux program that executes in the background ready to perform an operation when required. Functioning like an extension to the operating system, a daemon is usually an unattended process that is initiated at startup. Typical daemons are print spoolers and email handlers or a scheduler that starts up another process at a designated time. The term comes from Greek mythology, meaning "guardian spirit." See agent and mailer-daemon.
From the Greek daimon, meaning divine power. A utility that resides in RAM, waiting in the background until an event triggers it to take action. Print spoolers, e-mail handlers, and automatic backup utilities are examples of daemons. In mythology, a daemon was variously a guardian spirit or secondary divinity in the form of a demigod, i.e., half-man and half-god, that was tasked with duties deemed too insignificant for the gods' attention. See also RAM and utility.