A person with ‘AB’ blood group is sometimes called a universal recipient because of the

A person with AB blood expresses both A and B antigens on their red blood cells but does not produce anti-A or anti-B antibodies in their plasma. Because they lack these circulating ABO antibodies, AB individuals will not mount an immune reaction against donor red cells of types A, B, AB, or O, allowing them to safely receive red blood cells from any ABO type (the Rh factor must also be considered clinically). This absence of anti-A and anti-B antibodies is the reason AB is termed the “universal recipient” for red cell transfusions in the ABO system [1].

Sources

1. [1] https://www.redcrossblood.org/donate-blood/blood-types.html