Okay kiddo, so a millennium question is basically a big question that comes up when we enter a new millennium, which is a fancy word for 1000 years. Do you know what year we are in right now? That's right, we are in the year 2021. That means the last time we entered a new millennium was at the beginning of the year 2000.
When we entered the year 2000, people wondered if all the computers and technology we use in our daily lives would still work properly because they were programmed to only understand dates that started with 19 like 1990, 1995 etc. This is called the Y2K or Year 2000 problem. But luckily, all the necessary steps were taken before the new year began to make sure everything worked fine.
So, a millennium question is a big question that we think about when we enter a new millennium. It may relate to science, technology, society or any other fields. It's like starting a new book, and we wonder what new adventures and experiences will come our way. But don't worry, we will always find answers to our questions with the help of science and learning.