For battery factories specifically, the term is used for factories producing more than 1GWH per year. That was unusual before EVs became a thing. This particular factory is supposed to scale to about 60GWH capacity. That sounds like a lot but it's only a million 60KWH batteries that would go into e.g. a decent EV. With most ICE car production disappearing over the next two decades, we'll need a lot more factories.

Tesla has actually started talking about Tera factories a few years ago. That's roughly what they'd need to produce 20M such vehicles. And of course they have more need for batteries with their grid storage and truck business. So, it's easy to see how they'd end up with multiple tera factories if they keep on growing like they have been.

No. It has to be about 1000 times bigger than a Megafactory.