Rh-negative refers to the absence of the Rh factor, a specific protein found on the surface of red blood cells. This classification is part of the broader blood type system, which includes types like A, B, AB, and O. Individuals with Rh-negative blood do not have this protein, which can affect blood transfusions and pregnancy. 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 important for medical reasons, especially during pregnancy, as it can lead to complications if an Rh-negative mother carries an Rh-positive baby.