Persian Empire: A series of imperial dynasties centered in Iran. It's like if your book club became so popular it started ruling other local book clubs.
Zoroastrianism: An ancient pre-Islamic religion of Iran that survives there in isolated areas. Consider it as one of the oldest books still being discussed within this book club.
Farsi Language: The modern Persian language spoken in Iran today. Like the current favorite book being read by all members of this particular book club.