In a power system, each bus or node is associated with 4 quantities in the Newton-Raphson power flow method. These are:

1. Voltage magnitude (V): The magnitude of the voltage at the bus in volts.

2. Voltage phase angle (δ): The phase angle of the voltage at the bus with respect to some reference angle, usually taken as zero.

3. Real power injection (P): The net active power injection (or consumption) at the bus in megawatts.

4. Reactive power injection (Q): The net reactive power injection (or consumption) at the bus in megavolt-amperes reactive (MVAR).

These 4 quantities are known as the bus or node variables. In power system analysis using the Newton-Raphson method, the values of these variables are solved iteratively.