Okay kiddo, so imagine you look up at the sky and see a big, fluffy cloud. This cloud is called a cumulonimbus. It's special because it's really tall and can reach up to 30,000 feet in the air! That's like stacking 6 Empire State Buildings on top of each other!
Now, as the cumulonimbus cloud grows taller and taller, it gets colder and colder. This can cause the water droplets inside the cloud to freeze and turn into ice. The ice can stick together and make the cloud look like it has a flat top. This flat top is called an "incus."
So, when we say "cumulonimbus incus," we're talking about a really tall cloud with an icy, flat top. When you see a cumulonimbus incus, it means that there might be a storm coming. The cloud can produce rain, lightning, thunder, and even hail. So, if you see a cumulonimbus incus in the sky, make sure to stay safe and maybe even bring an umbrella with you just in case!