O blood type is one of the four main blood types in the ABO blood group system, which also includes A, B, and AB. Individuals with O blood type have neither A nor B antigens on the surface of their red blood cells. Instead, they have anti-A and anti-B antibodies in their plasma, making them universal donors for blood transfusions. People with O blood type can receive blood only from other O type donors. This blood type is the most common worldwide, with a significant presence in various populations. Understanding blood types is crucial for safe blood transfusions and organ transplants, as mismatched blood can lead to serious complications.