Erythrocytes, also known as Red Blood Cells (RBC) in blood tests, are the most abundant blood cells. They give blood its red color and contain the hemoglobin pigment, which transports oxygen to tissues and removes carbon dioxide. These cells are responsible for carrying oxygen, taken in through respiration, from the lungs to body tissues, a function they perform with the help of hemoglobin. Furthermore, they possess a flexible structure that allows them to move easily within blood vessels.