Frahang-i pahlavig is like a special book with secret words in ancient Persian language called Pahlavi. The book has a list of these words and tells you what they mean in Pahlavi, so you can understand what people were saying back in those days. It's like having a special codebook that helps you understand a secret language. People who study ancient Persia use it to help them learn more about the history and culture of the people who lived there a long time ago. They say it's like having a time machine that can take you back to the past and help you understand how people communicated and what they thought was important.