O형 (Blood) is one of the four main blood types in the ABO blood group system, characterized by the absence of A and B antigens on the surface of red blood cells. Individuals with O형 blood can donate to any other blood type, making them universal donors. However, they can only receive blood from other O형 donors. People with O형 blood are often thought to have certain health traits and personality characteristics, although scientific evidence is limited. This blood type is the most common worldwide, with a significant presence in various populations, including Asia, Europe, and Africa.