A part of the mind or brain. A Minsky agent, basically. I'm not sure my word is good but "agent" has its own problems (and Minsky himself gave it up for the very un-animistic "resources"). The end product of agential refactoring. An actor in the internal theater of the mind.
See of course Freud, Ainslie, Society of Mind, and too many other pages here to list. In fact don't I have an appropriate page for this concept already? Hm, no! Weird. It's too pervasive I guess.