Okay kiddo, have you ever heard of a special kind of light called fluorescence? You know how when you shine a light on certain things, like a flower or a rock, they don't look like they're glowing? Well, with fluorescence, they actually DO look like they're glowing because of some special molecules inside of them.
Now, one of these special molecules is called green fluorescent protein or GFP for short. It's a tiny protein that's found in certain types of jellyfish (yup, you read that right - jellyfish!). Scientists discovered GFP in the 1960s and figured out how to use it to make things light up nice and bright in different shades of green. They even made it useful by attaching it to other proteins!
GFP is made up of tiny building blocks called amino acids, which link together to form a long chain. At one end of the chain is a special group of atoms that absorb light - this is what makes GFP glow in the first place! And at the other end of the chain is another special group of atoms that lets GFP attach to other proteins.
So, scientists can use GFP in all sorts of cool ways. They can attach it to a specific protein in a cell or an animal, and then shine a special type of light on it to make it glow. This way they can study different processes, like how cells divide, how proteins move around inside cells, or how certain diseases work.
In short, green fluorescent protein is a special molecule found in jellyfish that can make other things light up green. Scientists use GFP to study different things in cells and animals.