Threshold of originality is a rule that artists and creators need to follow when they are making something new. It means that the thing they make has to be unique enough and different from other things that have already been made.
Imagine you're a kid and you want to draw a picture of a dinosaur. If you just copy someone else's drawing, that's not very creative. But if you draw your own dinosaur with your own colors and patterns, that shows your own creativity and imagination.
The same rule applies to adults who create things like music, movies, or books. They can't just copy someone else's work and try to pass it off as their own. They have to come up with their own ideas and make something that's different enough from other people's work.
It's important to follow the threshold of originality because it protects artists' rights and encourages creativity. Imagine if anyone could just copy someone else's work and claim it as their own. That wouldn't be fair to the original creator or to anyone else who wants to make something new.