Residual volume is the amount of air that remains in the lungs after a person exhales completely. This volume is important because it prevents the lungs from collapsing and ensures that there is always some air available for gas exchange, even between breaths. In healthy adults, the residual volume typically ranges from about 1 to 1.5 liters. It is a key component of lung capacity measurements, which also include other volumes like tidal volume and vital capacity. Understanding residual volume helps in assessing lung function and diagnosing respiratory conditions.