Question says it all, really. Brit here and my own research suggests that green onions are the straight type of spring onion whereas scallions tend to have a bulb at the end (we generally also call these spring onions in Britain, though occasionally I see them labelled as salad onions).
BUT I read a lot of US and dual edition recipe books and have only ever come across scallions.
I’m wondering if it might be a regional thing?