Okay kiddo, have you ever heard of the word "murder"? It means hurting or killing someone on purpose. And when we add "premeditated" to it, it means the person who did it planned it ahead of time.
Do you know what planning means? It means thinking about something you want to do, making a plan for how to do it, and then following through with that plan.
So, if someone thinks about hurting or killing another person for a while and makes a plan to do it, that's called premeditated murder. It's a very serious crime and can result in the person who did it going to jail for a long time or even life.
It's important to remember that hurting or killing somebody is never the right thing to do, and we should always try to solve our problems without hurting others.