The better one would be how the power is acquired. Throttle = motorbike. Pedals = bicycle.

In Europe at least, an e-bike can only provide pedal assistance up to 15.5mph, with a 250w maximum power limit (I think that's a class 1 in US). Anything that can be driven on just a throttle or above 15.5mph is a moped and needs a registration plate, insurance, tax etc.
There are plenty of illegal mods/imports, but they can be taken away by the police just for being on a road.

Why the US groups throttle controlled moped with e-bicycles is beyond me.