what is ment by potential difference /

Current is electrons moving through a substance, typically in a wire for our purposes. What makes the electrons move? To answer that, we need to review what we learned about electric potential.

Why is the water stored so high up? It took work to lift it up there. That work is stored as potential energy. When the water is allowed to flow down a pipe and out, it is moving fast because the potential energy has been converted to kinetic energy. Notice what matters here is the difference of the height at which it was stored and the height at which it is used.

Similarly, when charges have been separated, work was done. The stored energy per charge is the electric potential difference or sometimes just called the potential.