RBCs, red cells, haematids, erythroid cells or erythrocytes
Red blood cells, or erythrocytes, are the most common type of blood cell and the vertebrate organism's principal means of delivering oxygen (O2) to the body tissues via the blood flow through the circulatory system. They take up oxygen in the lungs or gills and release it while squeezing through the body's capillaries. These cells' cytoplasm is rich in haemoglobin, an iron-containing biomolecule that can bind oxygen and is responsible for the blood's red color. Red blood cells are also known as RBCs, red cells, haematids, erythroid cells or erythrocytes.