A Pressure Reducing Valve is used to obtain a desired downstream pressure. The valve is adjusted with that goal in mind.

The fact that a valve is adjustable does not necessarily make it a PRV. A balancing valve might be used to balance the flow in a circuit to a desired flow rate. They are not only used in bypass situations. They might also be used when there are a number of circuits coming into one common manifold, and one wants to obtain an equal pressure drop through each circuit (balance the circuits). The goal is different to the PRV.

Not sure on circuit setter, but sounds similar to balancing valve?

I agree with TechnoZA.  The purpose of a balance valve is to balance/control the flow in a particular branch or circuit.  Even in coil systems with two-way control valves (i.e., no bypass), you don't want the coils closest to the pump to get all the flow.  It's similar to manual volume dampers in HVAC duct systems.  It is probably true that the pressure is incidentally reduced through a balance valve.

The Circuit Setter is a registered trademark of ITT Bell & Gossett.  It is a balance valve.  The importance of getting balance valves or circuit setters vs. just a globe valve or something that you can throttle, is that it comes with integral valved read-out ports and a memory stop indicator.  That way you can measure the pressure differential across the device (like an orifice flow meter) and with a manufacturer-furnished chart establish the flow.  The memory stop is useful in that you can shut off the valve when necessary, but then you can return it to the the formerly balanced position when you want to put the circuit back in service.

Another brand name device you may have heard of by B&G is the "Triple Duty Valve".  This is more typically found at pump discharges.  This one valve can serve the function of three others (hence the name):  shut-off, check valve, and balance valve.