What is the name for the section of wall above kitchen cabinets?

If by "cabinets" you mean the upper cabinets, and those cabinets do not reach to the ceiling, the structure between the cabinets and the ceiling is usually called the soffit. But I don't know that there's a special term that refers to just the wall area between the top of the cabinets and the ceiling.

I think what you mean is a splash back but splash back would apply where there is water and there is no water above the upper cabinets. In the real world there is no real term for that void space above your cabinets so you can just call it the "Overhead Space"