Daemon

A daemon is a computer program that performs its function "in the background" during the normal operation of a computer system, for example providing security services, performing maintenance operations, communication with peripherals or other subsystems, or more.

The Terminals located on Installation 00 stated that daemons tried to prevent Mendicant Bias from communicating with John-117. He may have used the phrase to refer to other Forerunner artificial intelligences on Installation 00, or more likely uncontrollable background processes.

Trivia
Historically, daemons, not to be confused with demons, are good or malevolent supernatural beings between mortals and gods, such as inferior divinities and ghosts of dead heroes.