Rh negative refers to the absence of the Rhesus factor, a specific protein found on the surface of red blood cells. People with Rh negative blood do not have this protein, while those with Rh positive blood do. The Rh factor is important in blood transfusions and pregnancy, as it can affect compatibility between a mother and her baby. Approximately 15% of the global population has Rh negative blood, with higher frequencies in certain populations, such as those of European descent. Blood types are classified based on the presence or absence of the A and B antigens, along with the Rh factor, leading to eight possible blood types.