Imagine you and your friends took a really hard test. A percentile score is a way to see how well you did on the test compared to everyone else who took it.
Let's say you got a percentile score of 80. That means you did better than 80% of the people who took the test!
It's kind of like ranking how good you did. If you got a higher percentile score, that means you did better than most of the other people who took the test. If you got a lower percentile score, that means you didn't do as well as most of the other people who took the test.
Percentile scores can be shown on a graph that looks like a really long bar. The higher your score, the farther to the right your dot will be on the graph. The lower your score, the farther to the left it will be.