What is voltage also known as?

The term, 'voltage', is synonymous with 'potential difference'.

Originally, the term 'voltage' was used to describe potential difference when specifcally expressed in volts. These days, however, we use the term whatever multiples or submultiples of volts are used -so it applies to potential difference whether expressed in microvolts, millivolts, volts, kilovolts, megavolts, etc.

It's very important to understand that voltage is synonymous with 'potential difference', and not'potential'. So it would be quite incorrect to describe, say, the 'voltage at a point' in a circuit (e.g. "...the voltage at point A in a circuit is +12 V").