The best description is that
The best description is that the Prius PHEV "might" drive solely on electricity for up to 13 miles. It is still designed to use a combination of electricity and gasoline (at any time) to get the most efficient propulsion possible. We can all agree that the Volt "not" designed like this, so why should it have the same name?
As far as series hybrid.....
A better example of a series hybrid is a Diesel Electric Locomotive. The diesel engine generates electricity which is applied directly to an electric motor to drive the train. There is no battery in this topology so the train cannot move if the engine is not running. The reason for this design is that the instant torque of the electric motor helps the train to move more quickly than a straight diesel engine could.....Once again.....The Volt is not designed like this, so why should it have the same name?
The Volt is conceptually an improved EV1 with a Lithium battery and a range extender added.
GM did not invent the term "range extender" with the Volt. GM already had a device that they called a range extender that was used with the EV1 for testing. It was a generator on a trailer that was cabled to the EV1 charge port. Turn the generator switch on and it recharged the EV1 battery to allow the EV1 to continue to operate indefinitely without stopping to recharge. This allowed GM to test the EV1 24 X 7.
GM "actually considered" putting the range extender in the EV1, but decided against it, going for a pure EV instead. Who knows how much differently things might have turned out if they did....
With the Chevy Volt, GM learned their lesson and added the range extender/generator. They simply took the range extender off the trailer and put it under the hood.
So...... GM did not invent the term EREV just to be different than a PHEV or series hybrid. EREV describes exactly what GM designed when they built the Volt.