Expiratory Reserve Volume (ERV) is the amount of air that can be forcibly exhaled after a normal exhalation. It represents the additional volume of air that can be expelled from the lungs beyond the typical breath. ERV is an important measure in assessing lung function and can help identify respiratory conditions. Measuring ERV is typically done using a spirometer, a device that records the volume of air inhaled and exhaled. Understanding ERV, along with other lung volumes like Tidal Volume and Inspiratory Reserve Volume, provides valuable insights into overall respiratory health and efficiency.