Voltage

The push.

Potential difference

Voltage is the energy given to each unit of charge, and it exists between two points rather than at one. That is why a bird on a single wire is unharmed.

A battery maintains a fixed potential difference until it runs down.
Mains voltage is 230 volts in much of the world and 120 in North America.

The water analogy

Pressure is voltage, flow rate is current, and a narrow pipe is resistance. It breaks down eventually, and it carries you a long way first.