Okay, so you know how some kids get sick with things like the flu or chickenpox? Well, there are some kinds of sicknesses that hardly anyone gets, and those are called orphan diseases. It's kind of like if you were a kid with a cold and your friends didn't have it too- that would be really unusual, right?
Orphan diseases are usually really rare and can affect things like the way your body works, the way you think or move, or even things like your skin or hair. Sometimes, only a few people in the whole world have these kinds of diseases!
The reason they're called "orphan" diseases is that they don't get as much attention as other kinds of illnesses. It's kind of like they're like orphans who don't get as much love as kids who have lots of family and friends around them. Because the diseases are so rare, there isn't as much money or research being put into figuring out how to help people who are sick with them.
But even though they don't get as much attention, there are still doctors and scientists who are working really hard to find out more about these orphan diseases, so that they can help people who are sick with them. Sometimes, they even discover new treatments and cures that can help people feel better!