O Negative is a blood type characterized by the absence of A and B antigens on the surface of red blood cells, along with the absence of the Rh factor. This means that individuals with O Negative blood can donate to any other blood type, making them universal donors. However, they can only receive blood from other O Negative donors. People with O Negative blood make up about 7% of the population. This blood type is particularly important in emergency situations where there is no time to test a patient's blood type. Hospitals often keep O Negative blood on hand for transfusions, especially for trauma patients.