The fundus is like the back part of the eye that you can't see from the outside. It's like a secret room in the eye where a doctor or nurse might go to check if everything is okay with your eyes.
It's a special part of the eye that has some important things inside, like the retina and the optic nerve. The retina is like the screen of a movie theater, where pictures and colors are shown. The optic nerve is like a big cable or wire that sends these pictures and colors to your brain, so you can see.
When someone checks your fundus, they might use a special flashlight that's very bright. They will ask you to look straight ahead while they shine the light into your eye. They might wear a special looking glass to see inside your eye better.
If everything looks good in your fundus, it means that your eyes are healthy. But if something looks different, like a bump or a hole, the doctor or nurse might need to do more tests to make sure everything is okay.