Gamma rays are a type of light, kind of like the sparkly stuff you see in the sky sometimes at night.
An ultra-high-energy gamma ray is like a super-powered version of a regular gamma ray. It has a lot more energy than normal gamma rays, which means it can do some really cool and important things.
For example, ultra-high-energy gamma rays can be used to study things that are really far away in space, like stars and galaxies. They can also be used to look for tiny particles called neutrinos, which are super hard to detect normally.
Scientists study ultra-high-energy gamma rays using special tools called telescopes. These telescopes are like really big cameras that can take pictures of the gamma rays. By looking at these pictures, scientists can learn more about the Universe and how it works.