The canonical inquisition was a big investigation that happened a long time ago in the Catholic Church. The Church wanted to make sure that everybody who believed in God was following the rules and doing things the right way. So, they sent special people called inquisitors to go and talk to people and ask them questions about their beliefs and practices.
Sometimes, the inquisitors thought that maybe people were doing things that weren't allowed, so they would ask more questions to figure out if the people were doing something bad. If they found out that the people were doing something wrong, they would tell them to stop and explain what they needed to do right.
This was really important to the Church because they wanted to make sure that people were doing things in a way that would make God happy. Even though it may seem like a big and scary thing, the canonical inquisition was just a way for the Church to make sure that everyone was following the rules and being the best they could be for God.