- blood group, blood type - people whose blood (usually just the red blood cells) has the same antigens
--1 is a kind of people
--1 has particulars:A, type A, group A; B, type B, group B; AB, type AB, group AB; O, type O, group O; Rh-positive blood type, Rh positive; Rh-negative blood type, Rh-negative blood, Rh negative