Imperium is a big, fancy word that essentially means power or control. It's like when a grown-up is in charge and makes all the decisions, but on a really big scale. Imagine you're playing a pretend game with your friends, and one friend gets to be the "boss" or "leader" who tells everyone what to do. That's kind of what imperium is, but instead of just a pretend game, it's something that happens in real life with countries or groups of people.
For example, a long time ago in ancient Rome, there was a group of people called the "senators" who had imperium over the rest of the people in their empire. This meant they were the ones who made the decisions about laws and things that affected everyone else. Think about your teacher telling you what to do in class, but on a much bigger level.
The concept of imperium can apply to many different situations. It can refer to a government having power over their citizens, or a boss having power over their employees. It can even apply to things like your mom having imperium over your allowance or what you have for dinner.
Overall, imperium just means having control or power over others, and it can be a complicated idea to understand fully. But just remember, it's like being the boss in a game of pretend, except it's for real and affects a lot of people.