A blood group is a classification of blood based on the presence or absence of specific antigens on the surface of red blood cells. The main blood group systems are ABO and Rh, which determine whether a person's blood type is A, B, AB, or O, and whether it is positive or negative, respectively. These classifications are crucial for blood transfusions, organ transplants, and pregnancy. Understanding blood groups is essential for medical procedures. For instance, receiving incompatible blood can lead to serious health complications. Therefore, knowing your blood group helps ensure safe medical treatments and can also provide insights into certain health conditions and genetic traits.