Avestan is an ancient language that was spoken a very, very long time ago by people who lived in a place called Iran. Just like how we speak English today, Avestan was the language that these people used to communicate with each other. It's different from the language we speak now because it has a different alphabet and sounds different.
One really special thing about Avestan is that it was used to write down important religious texts. These texts were called the Avesta and they included things like prayers and stories about the gods that these people believed in.
Even though nobody speaks Avestan today, we can still read it and learn from it because people wrote it down on special materials that last a really long time. By studying Avestan, we can learn more about what life was like a long time ago in Iran and what people believed in.