Okay kiddo, have you ever played a game where you have to find a hidden object and your mom or dad tells you if you are getting closer or farther away from it? The deflationary theory of truth is kind of like that game.
It's the idea that the word "true" doesn't really mean anything special or describe anything about the world around us. Instead, it's just a short way of saying something simpler like, "yep, that matches up with what we know or believe."
So, let's say you ask me if it's raining outside and I say "yes, it's true." What I'm really saying is that my answer "yes" matches up with what we believe or know about the current weather, not that "truth" is a big important thing on its own.
The deflationary theory suggests that we don't need to get all philosophical or complicated about the meaning of true, because really it's just a shortcut way of saying, "yep, that checks out."