Blood type O is one of the four main blood types, classified by the presence or absence of specific antigens on the surface of red blood cells. Individuals with blood type O do not have A or B antigens, making them universal donors. This means they can donate blood to any other blood type, which is crucial in emergency situations. People with blood type O can receive blood only from other type O donors. This blood type is also associated with certain health traits, such as a lower risk of heart disease. Understanding blood types, including blood type O, is essential for safe blood transfusions and organ transplants.