Peninsula in Russian region son overlooked (6)
I believe the answer is:
Here is my best explanation:
'peninsula' is the definition.
(Iberia is an example)
I can't explain the rest of the clue.
(Other definitions for iberia that I've seen before include "European region", "Spanish/Portuguese peninsula", "Peninsula that was Roman province", "Peninsula housing Spain and Portugal", "Great European peninsula containing Spain and Portugal", "The Spanish peninsula", "Peninsula comprising Spain and Portugal", "Spain and Portugal together", "European territory" and "Spain's national flag-carrying airline".)