human blood cells (usually just the red blood cells) that have the same antigens
A classification of blood that is based on the presence or absence of antigens in the red blood cells of an individual. For the purposes of blood transfusion three antigens referred to as "A", "B" and "RhD" (out of a total of 29) are the most important. Based on their presence the human blood can be classified to A, AB, B, and O blood types which are further divided to Rh positive or negative.