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 is Rh negative, with higher frequencies in certain populations, such as those of European descent. Knowing one's Rh status is crucial for medical procedures, as incompatible blood transfusions can lead to serious health complications.