You are in the virtual presence of a Sage who knows his onions.
Onion is known botanically as Allium cepa. There are many varieties:
There are Cipollini Onions
There are Spring onions, or Scallions
There are Leeks
There are Pearl Onions
There are Red Onions or Bermuda Onions
There are shallots
There are Sweet Onions of several varieties, such as Maui, Vidalia and Walla Walla.
There are white onions
…And the very common Yellow Onions also known as Brown Onions.