usr originally contained user files (http://cm.bell-labs.com/cm/cs/who/dmr/notes.html http://cm.bell-labs.com/cm/cs/who/dmr/notes.html). I'm not really sure wh

usr originally contained user files (http://cm.bell-labs.com/cm/cs/who/dmr/notes.html http://cm.bell-labs.com/cm/cs/who/dmr/notes.html). I'm not really sure why or when that changed, but supposedly "Unix System Resources" is a backronym.