Why is type O blood called "panda blood"?

Blood type O is not actually referred to as "panda blood," which is a common misconception. "Panda blood" actually refers to Rh-negative blood. It is called "panda blood" because its rarity resembles that of the giant panda. Rh-negative blood and type O blood belong to different blood group systems: Rh-negative blood belongs to the Rh blood group system, while type O blood belongs to the ABO blood group system. The ABO blood group system classifies blood types based on the presence or absence of A and B antigens on the surface of red blood cells, including four types: A, B, AB, and O. The Rh blood group system, on the other hand, classifies blood types based on the presence or absence of the D antigen on red blood cells. Blood types that have the D antigen are classified as Rh-positive, while those lacking the D antigen are classified as Rh-negative.