The "tagged" part is important. They are in fact not called "unions" in most languages, only C-derived languages. And in C, unions are untagged. Only later exte

The "tagged" part is important. They are in fact not called "unions" in most languages, only C-derived languages. And in C, unions are untagged. Only later extensions added tagged union types. So I would contend that unqualified "union type" means an untagged union.