Yes, it's known as the 'sense' input. It allows the voltage regulator inside the alternator to get a more accurate indication of battery voltage, without being fooled by the voltage drop through the main output wire. But many alternators just sense their own output and ignore the drop through the wiring, hence they don't have the 'sense' input.
The difference is small, usually unnoticeable. Mostly useful in cold weather, IMO, where starting takes a lot out of the battery and loads tend to be high (always running heater, lights, wipers). Without the sense input, it takes a bit longer to fully recharge the battery.