O Rh positive is a blood type characterized by the presence of the Rh factor, a protein on the surface of red blood cells. It is one of the most common blood types, meaning many people have it. The "O" indicates that there are no A or B antigens present in the blood, making it a universal donor type for red blood cells. Individuals with O Rh positive blood can receive blood from O Rh positive and O Rh negative donors. This compatibility is crucial in medical situations like blood transfusions or organ transplants, where matching blood types can prevent serious complications.