From IFWiki

Generally, a routine called every turn regardless of what the player has done. Daemons can be used to automate autonomous NPC behavior; for events asynchronous to the player; and for events that must occur after a certain number of turns.

Daemons have control over what happens in game without specifically controling the player. A timer (or fuse) is a specific type of daemon.

In Inform 6, a daemon is an interfering spirit associated with a particular game object, which gets a chance to interfere while it is "active".

See also: