Anemia; also spelled anaemia and anæmia; from Greek ἀναιμία anaimia, meaning lack of blood) is a decrease in number of red blood cells (RBCs) or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin deficiency.