I've always divded the line by saying that a 4x4 is anything with a "low" setting, such as the 4Runner my father now drives. In order to qualify as AWD, at least the way I've been thinking of things, the system must be engaged full time, lack a low range, and usually biases one set of wheels under normal conditions. Such as in my father's A4, or my mother's RX300 which biases the front wheels in a 60/40 split untill slippage occurs.