Deoxygenated blood is blood that has a low level of oxygen and a high level of carbon dioxide, making it less red in color compared to oxygen-rich blood. This type of blood is essential for the body's circulatory system, as it carries waste products from the tissues back to the heart and lungs for reoxygenation. Understanding the movement of deoxygenated blood is crucial in comprehending how systemic and pulmonary circulation work together to maintain oxygen supply and carbon dioxide removal in the body.