Okay, kiddo! Let's say we have a street with lots of houses on it. Now, if we look at all the houses on the street, there's usually one house that's in the middle of all the other houses. That's called the house in the middle.
The house in the middle is different from the other houses in a few ways. For example, it might have more neighbors than any other house on the street. Or, it might be the only house that's not on a corner.
Now, you might be wondering why it's called the house in the middle. That's because it's literally in the middle of all the other houses on the street. It's like the center of a circle with all the other houses spread out around it.
So, that's what the house in the middle means. It's just a term that we use to describe the house that's in the middle of all the other houses on a street.