The ABO group is a system of blood groups that categorizes blood based on the presence or absence of specific antigens on the surface of the red blood cells. Some synonyms for ABO group include blood type, blood group, and blood classification. Other terms used to refer to specific ABO groups include A-positive, A-negative, B-positive, B-negative, AB-positive, AB-negative, and O-positive and O-negative for the universal donor and the universal recipient blood types, respectively. Understanding one's ABO group is crucial in blood transfusions, organ donations, and medical procedures, as incompatibility can result in severe reactions, such as a transfusion reaction or transplant rejection.