What is the medical term for the notch in the inner medial border of the kidney?

The term you're looking for is "Hilum," which specifically refers to the area on the medial (inner) border of the kidney where various structures, such as blood vessels, nerves, and the ureter, enter and exit. This notch plays a crucial role in the kidney's functionality because it is the gateway for the renal artery and vein, as well as the ureter, facilitating the essential flow of blood and urine.

While "Cortex" refers to the outer layer of the kidney involved in filtering blood and forming urine, and "Medulla" refers to the inner region composed of renal pyramids that also contribute to urine production, neither of these is a notch or indentation. The "Pelvis" is the central cavity of the kidney that collects urine before it moves to the ureter, but again, it does not describe the specific notch in the kidney's border. Hence, "Hilum" is the correct term that directly describes that particular anatomical feature.