In computing, a daemon is a background process that handles tasks without the user’s direct input. Print daemons spool up documents to be printed, HTTP daemons return data to the web browser issuing the inquiry, task scheduling daemons fire off tasks when the clock triggers them, and so on.
These daemons derive their name, in a roundabout way, from Greek mythology. During the 1960s, programmers working on Project MAC (Mathematics and Computation) at MIT’s Computer Science and Artificial Intelligence Laboratory were searching for an appropriate name for the background processes they were creating that carried out functions with no input from the user.
They decided to call the background processes “demons” after Maxwell’s demon—an imaginary being from James Clerk Maxwell’s 19th century thought experiment that was responsible for the sorting of molecules in Maxwell’s theoretical chamber. Maxwell had, in turn, called his little thought experiment helper a demon as a nod to the daemons of Greek mythology—supernatural beings (helpers) who carried out tasks for the gods.
Although the spelling reverted from demon to the more traditional daemon over the years, the term stuck. Just like the Greek daemons helped carry out tasks quietly in the background, modern computer daemons continue the tradition of quiet and invisible assistance.