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 remainder of the clue.
(Other definitions for iberia that I've seen before include "Overpower, overwhelm", "Spain and Portugal - airline", "Spain and Portugal (6)", "West European peninsula", "Peninsula comprising Spain and Portugal", "Peninsula housing Spain and Portugal", "Great European peninsula containing Spain and Portugal", "Spain's national flag-carrying airline", "Spain and Portugal together" and "Peninsula encompasing Spain and Protugal".)