A program which is often started at the time the system boots and runs continuously without intervention from any of the users on the system. The daemon program forwards the requests to other programs (or processes) as appropriate. The term daemon is a Unix term, though many other operating systems provide support for daemons, though they’re sometimes called other names. Windows, for example, refers to daemons and System Agents and services.
Daemon is the Latin word for the Ancient Greek daimon (δαίμων: "god", "godlike", "power", "fate"), which originally referred to a lesser deity or guiding spirit such as the daemons of ancient Greek religion and mythology and of later Hellenistic religion and philosophy.
The word is derived from Proto-Indo-European *daimon "provider, divider (of fortunes or destinies)," from the root *da- "to divide". Daimons were possibly seen as the souls of men of the golden age acting as tutelary deities, according to entry δαίμων at Liddell & Scott.
