AB blood is one of the four main blood types in the ABO blood group system, which also includes A, B, and O. Individuals with AB blood have both A and B antigens on the surface of their red blood cells, making them universal recipients. This means they can receive blood from any ABO type without experiencing an immune reaction. People with AB blood can donate to other AB individuals but can only receive blood from A, B, AB, and O types. This unique combination makes AB blood relatively rare, occurring in about 4% of the population.