When you boil it down, NEUMORPHISM is a focus on HOW LIGHT MOVES in three-dimensional space.
There are, he suggests, two key differences between skeuomorphism and neumorphism.
First, neumorphic elements don’t have to represent real-world objects. They are simply three-dimensional shapes which can have arbitrary designs.
Second, while a skeuomorphic icon exists in isolation – the shadow patterns might vary from its neighbouring icons – neumorphism is all about a consistent light pattern across the entire screen. If the light is coming from top left for one icon, it must be coming from top left for all the other icons on the screen.