Physiol. a classification of human blood based on the presence on the surface of red blood cells of one or both of two specific antigens, designated A and B, or their absence, designated O: every person has one of four possible inherited blood types, A, B, AB, or O, and has antibodies circulating in the blood that clump with any antigen that is not of that type, persons with type O thus being able to donate blood devoid of the antigens for transfusion to types A, B, and AB but able to receive only blood of type O.
[ 1940-45 ]