Iceland
Some Icelandic IP keeps adding Iceland to the core definition, as if this was the widely accepted position. Iceland is not part of Scandinavia per the most common definition, and needs to be mentioned in the context of the extended usage only. Even though Iceland was largely (but not exclusively) populated by people from what became known as Scandinavia a millennium later, Iceland as a country is not part of Scandinavia, just like Australia is not part of England even though its population is mostly descended from English people and speaks English. What makes Scandinavia, a term that entered usage in the 18th and 19th centuries, a relevant entity, is the common (mutually intelligible) language, which Iceland is not part of.