Why is the delta region to the north called Lower Eygpt

The terminology "Upper" and "Lower" derives from the flow of the Nile from the highlands of East Africa northwards to the Mediterranean Sea, the opposite of a north - to-south flowing river like the Mississippi. Lower Egypt mostly consists of the Nile Delta.

That area is called lower Egypt because it is physically lower than the rest of Egypt. That's also why the Nile River flows to the North.