Okay, so have you ever played with Play-Doh before? Claypan is kind of like that, but it's outside and way bigger.
So, claypan is a layer of soil that has a lot of clay in it. Clay is a type of soil that's really sticky and makes things like pots and sculptures. But when it's in the ground, it can make it really hard for water and air to get through.
In some places, like certain areas in Australia, the soil has so much clay that it forms a layer that's really thick and hard. When it rains, the water can't sink into the ground very easily, so it just sits on top of the claypan.
This can be a big problem for plants and animals that need water to survive. But sometimes, when the water sits on the claypan for a while, it can form a little pond or lake. So, even though it's not great for everything, the claypan can also be a source of water in dry areas.
Overall, claypan is just a type of soil with a lot of clay in it. It can make it hard for water and air to get through, but it can also provide a water source in some areas.