Have you ever had three things in front of you and had to decide which one you like the best? That's kind of like what we call a "three-way comparison". It's like a game where you have to pick the best thing out of three things.
Sometimes we have to do that when we're trying to figure out which thing is better or worse than the others - like which ice cream flavor we like best, or which movie we want to watch.
So, let's say you have three different ice cream flavors in front of you: chocolate, vanilla, and strawberry. You have to decide which one you like the best.
First, you take a little taste of the chocolate flavor. Then, you take a little taste of vanilla, and then you take a little taste of strawberry. After you taste all three, you think about which one you liked the most.
Maybe you liked the chocolate flavor the best, so you say "Chocolate is my favorite!" Or, maybe you liked the strawberry flavor the best, so you say "Strawberry is my favorite!"
That's what a three-way comparison is - when you have three things to compare and you have to decide which one is the best. It's kind of like a game and it helps you decide which thing you like more than the others.