Type O blood is one of the four main blood types, classified by the presence or absence of specific antigens on the surface of red blood cells. It is characterized by the absence of both A and B antigens, making it a universal donor type. This means that individuals with Type O blood can donate to any other blood type, which is crucial in emergency medical situations. People with Type O blood can receive blood only from other Type O donors. This blood type is the most common worldwide, with approximately 45% of the population having it. Understanding blood types, including Type O, is essential for safe blood transfusions and organ transplants.