Okay kiddo, let's talk about "in re primus."
When grown-ups say "in re primus," they usually mean a legal case or proceeding that's all about something called "primus." Primus could be a person, a company, or something else that's being talked about in the case.
You see, sometimes grown-ups need to go to court to figure out who should get what, or who did something that wasn't allowed. When they do that, they might use Latin words like "in re" to talk about what the court case is about.
Now, when someone says "in re primus," it usually means they're talking about a specific case or legal proceeding where "primus" is the main topic. It's kind of like when you play a game and the main character is called the "protagonist."
Does that make sense, kiddo?