The idea that people you know well (those in your "monkeysphere") are more important to you than others (those outside your "monkeysphere")
For more information see article at www pointlesswasteoftime com / monkeysphere.html
That's why they don't mind stealing your stereo or vandalizing your house or cutting your wages or raising your taxes or bombing your office building or choking your computer with spam advertising diet and penis drugs they know don't work. You're outside their Monkeysphere. In their mind, you're just a vague shape with a pocket full of money for the taking.
The limited capacity of primates to conceptualize others as distinct and relevant individuals (from an article on Cracked.com). Studies suggest that for humans this limit is about 150 people, and those outside the monkeysphere are not really considered people at all, but one-dimensional bit characters.
Used as a term of endearment ("You are totally in my monkeysphere, baby") or indifference ("Did you hear about the mudslides in Argentina?" "Dude, that's way out of my monkeysphere. Who cares...").
The group of people you conceptualize as individuals & can empathize with. All humans outside of it are more or less just a walking bag of flesh, blood & bones that just so happen to be the same species as you. The maximum number of people that can be kept in a monkeysphere is estimated to be around 150.
Person 1: Look at that nerd!
Person 2: Hey! That's STEVEN.
Person 1: You know him?
Person 2: Yeah, he's in my monkeysphere.
Person 1:......Your what now?