Your country of residence is the country where you live when you start using your Pass. All countries previously appearing only on the Eurail website are now available in the drop-down menu during checkout on the Interrail website.
The country you select as your country of residence will appear on your Pass. If it doesn't match your identification documents, during your trip, you'll need to carry official government-issued proof that shows you're a resident of that particular country. For more information, please see Article 5 of the Interrail Pass Conditions of Use.