"Группа крови" (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 group systems are ABO and Rh. The ABO system categorizes blood into four types: A, B, AB, and O, while the Rh factor determines if the blood is positive or negative. Knowing one's blood type is crucial for medical procedures such as blood transfusions and organ transplants, as incompatible blood types can lead to serious complications. Blood type can also play a role in pregnancy, where the compatibility between the mother and fetus is important for health outcomes.