There is no universal blood type, but there is a universal donor type and a universal recipient type. Blood type O-negative is the universal donor type, while AB-positive is the universal recipient type.
Four main types of blood exist: A, B, AB and O. These types are then divided into negative blood and positive blood. Those with negative blood do not have the Rh factor, while those with positive blood do. People with positive blood types can receive either positive or negative blood, but those with negative blood can receive only negative. A person with type-A blood can receive a transfusion of either A or O, and those with type-B blood can receive either B or O. Those with AB can receive A, B, AB or O, but those with type O can receive only O. A person who has AB-positive blood can accept any blood type, positive or negative. A person with type O-negative blood can donate to any person, regardless of blood type.