EGM96 is a really detailed map of the earth that shows all the bumps and dips in the ground. It's like when you draw a picture and try to make everything look 3D by shading areas to show where they stick out and where they go in.
Scientists used special tools to measure the height of the ground all around the earth and put all that information into the EGM96 map. It's kind of like a big puzzle that they put all the pieces together to make the picture of the earth's shape.
This map is really useful because it helps people know where different things are on the earth and how to get from one place to another more easily. It also helps scientists study things like earthquakes and volcanoes to learn more about how they happen and how to keep people safe.