Calciopoli is a thing that happened in Italy a long time ago, when a bunch of important people who were in charge of the soccer teams did some naughty things. They were very dishonest and cheated in many different ways, like secretly talking to each other and deciding which teams would win and which teams would lose.
This was very unfair for the other teams who played by the rules and tried to win fairly, because they didn't have a chance to do well. It was kind of like if you were playing a game with your friends, and your friend kept changing the rules so that they could always win.
People found out about what these important people were doing, and they got in trouble for being so sneaky and dishonest. It was a very big deal in the soccer world, because it meant that important people who were supposed to be fair and honest were actually doing things that were very wrong.
After that, many things changed in the way that soccer was run in Italy. People worked very hard to make sure that everyone played by the same rules and that nobody cheated again. It was a good lesson for everyone to learn about why it's important to play fair and be honest, both in soccer and in life.