RhD refers to a specific protein found on the surface of red blood cells, which is part of the Rh blood group system. Individuals who have this protein are classified as Rh-positive, while those who lack it are Rh-negative. The presence or absence of the RhD protein is important for blood transfusions and pregnancy, as it can lead to immune reactions if mismatched blood types are mixed. The RhD factor is inherited from parents and is determined by genetics. It plays a crucial role in determining a person's blood type, which is essential for safe medical procedures. Understanding RhD is vital for preventing complications during blood transfusions and managing conditions like hemolytic disease of the newborn.