O positive is one of the eight main blood types in the ABO blood group system. It is characterized by the presence of the Rh factor and the absence of A and B antigens on the surface of red blood cells. This makes O positive a universal donor for plasma, meaning it can be given to patients of any blood type in emergencies. Individuals with O positive blood can receive blood from O positive, O negative, A positive, and A negative donors. This blood type is the most common in many populations, making it crucial for blood banks and transfusions. Understanding blood types is essential for safe medical practices and effective blood transfusions.