Spain and Portugal or vast region of Russia? Not initially (6)

I believe the answer is:

iberia

I'm a little stuck... Click here to teach me more about this clue!

'spain and portugal' is the definition.
(I've seen this in another clue)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for iberia that I've seen before include "Old name for Spanish peninsula" , "Where Juan possibly lives" , "old part of Europe" , "Spain and Portugal (6)" , "Spanish/Portuguese peninsula" .)

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