Prav-Yav-Nav is a way of describing how people use words and language to talk about things. Think of it like a secret code that we use with each other to help us understand what we're talking about.
"Prav" means something is true or correct. So if I say "the sky is blue" and you agree with me, you might say "yes, that's prav."
"Yav" means something is not true or incorrect. So if I say "the sky is purple" and you know that's not right, you might say "no, that's yav."
"Nav" means something is unknown or uncertain. So if I ask you a question like "what color are unicorns?" and you don't know the answer, you might say "I'm nav, I don't know."
So basically, Prav-Yav-Nav helps us communicate with each other so we can understand what's true, what's not true, and what we're not sure about. It's like a special language that grown-ups use to talk about things.