“No load voltage” is a common term used for unregulated power supplies, generators, and batteries. We define the no-load voltage \(V_0\), the electric potential difference present at the ends of a dipole, or a port, when the current flowing through it is zero, or when the two terminals of the port are disconnected from the electric circuit. It is the output voltage when nothing is connected to the output.
The higher the current, the lower the voltage. This is due to the supply’s internal series impedance. When nothing is connected to the output of the power supply (“no-load”), the current is 0 A, and the voltage will be at its highest. So the “no-load voltage” is the highest voltage the power supply will produce.