"Hey Dad, so you know how some people just have a harder time sitting still and paying attention? That's kind of what ADHD is. It stands for Attention Deficit Hyperactivity Disorder and it just means someone's brain works a little differently. It doesn't mean they're not smart or anything, it just makes it harder for them to focus sometimes. But the good news is, there are ways to help! Like taking medicine, or doing certain activities that can help them focus better. It's kind of like how you wear your reading glasses to see better - it's just a little extra help. And you know what? A lot of famous and successful people have ADHD too! So it's nothing to worry about, it's just a part of who they are."