Okay kiddo, imagine you're playing with a frisbee. Instead of throwing it like a normal person, you're going to throw it really hard straight down towards the ground. What happens? It hits the ground and bounces back up, right?
Now, imagine putting your hand behind the frisbee as you throw it down. You're not touching the frisbee, but your hand is close enough to it that it almost looks like you're high-fiving it as it goes by. This time, when the frisbee hits the ground, it doesn't bounce back up as much. It's like your hand slowed it down a little bit.
The part of the frisbee that's closest to your hand is called the trailing edge. And when you have something moving through the air (like a frisbee, or even an airplane wing), the trailing edge is the part that's at the back.
So, when we talk about the trailing edge of an airplane wing, we're talking about the part at the back of the wing. That part is really important because it helps control the airflow over the wing. If the trailing edge is shaped a certain way, it can make the airflow go exactly where the pilot wants it to go, which helps the plane fly more smoothly and efficiently.
I hope that helps, kiddo!