Group O – has neither A nor B antigens on red cells (but both A and B antibody are in the plasma); Blood group O - an universal RBC donor.

http://www.redcrossblood.org/learn-about-blood/blood-types.html

Group O has neither A nor B antigens on red cells (but both A and B antibody are in the plasma); Blood group O - an universal RBC donor and O group is universal recipient for Plasma and platelets.while reverse is true for AB group.

@Dharmesh Chandra Sharma,

So when transfusing O blood, the antibodies in O wouldn't affect the recipient blood?

Generally does not affected becuase is low amount of plasma, it can be different if transfusions are repeated many times in a short period

Group O persons are universal RBC donors. Plasma is transfused, if at all, in low amounts, that too if the antibody titer is low. The benefit of transfusing O red cells far exceeds the slight damage that may be caused by low titer antibodies present in the plasma. O red cells have neither A nor B antigens and , therefore, will not react either with anti-A nor with anti-B of Group B and Group A recipients respectively. Group AB persons are universal recipients because their plasma contains neither anti-A nor anti-B antibodies.