What is on top of that?

On top of that is a phrase that is commonly used in English. It indicates an additional point that is to be added to a preceding statement or situation. It is often used to indicate something that is being piled up or added to something else. The phrase is commonly used to add emphasis and to stress the point that is being made. It is an expression that is commonly used in both spoken and written English and is considered to be part of everyday language. Overall, "on top of that" is used to convey the sense of addition, accumulation, and emphasis.