Blood type refers to the classification of blood based on the presence or absence of specific antigens on the surface of red blood cells. The main blood types are A, B, AB, and O, which are determined by the type of antigens present. Additionally, each blood type can be either Rh-positive or Rh-negative, depending on the presence of the Rh factor. Blood type is important for blood transfusions, organ transplants, and pregnancy, as incompatible blood types can lead to serious health complications. Knowing one's blood type can also provide insights into certain health risks and compatibility with potential donors or recipients in medical situations.