So, let's say there's a big group of people who are playing a game together, and they want to make some rules to make sure everyone plays fairly. The person in charge of the game might make a list of rules called "act of sederunt."
This list of rules will explain how the game should be played, who can play, what kind of things are not allowed, and what will happen if someone breaks the rules.
It's important that everyone playing the game follows these rules, so that everyone has fun and no one gets hurt or feels left out.
Just like in this game, sometimes grown-ups in charge of things like courts or legal systems make a list of rules called "act of sederunt," to make sure everything runs smoothly and fairly for everyone involved.