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. Individuals with Type O blood do not have A or B antigens, making it a universal donor type. This means that Type O blood can be given to people with any other blood type in emergency situations. Type O blood is further divided into two subtypes: O positive and O negative. The Rh factor determines whether the blood is positive or negative. Approximately 37% of the population has Type O positive blood, while about 6% has Type O negative blood, which is especially valuable in transfusions due to its compatibility with all blood types.