Okay kiddo, forecast skill means how good someone is at predicting what will happen in the future. It's kind of like trying to guess if it's going to rain tomorrow or if it will be really sunny outside.
People like weather forecasters, sports analysts, and economists all use forecast skill to try and make the best predictions they can about what will happen next. They look at past patterns and data, use fancy tools and computer programs, and try to understand what's going on in the world around them to make their predictions.
Imagine you were trying to guess how many marbles were in a jar. You could use what you know about how big the jar is and how many marbles you've seen in jars before to make your guess. If you get it right, you've shown good forecast skill!
But sometimes it's really hard to predict what will happen. For example, no one could have predicted the coronavirus pandemic would happen and change the world the way it did. So even though people use forecast skill, it's not always perfect and unexpected things can happen.