A spirometer is a medical device used to measure the volume of air inhaled and exhaled by the lungs. It helps assess lung function and can be crucial in diagnosing respiratory conditions such as asthma, chronic obstructive pulmonary disease (COPD), and other lung diseases. During a spirometry test, a person breathes into the spirometer, which records the amount and speed of air flow. The results provide valuable information about lung capacity and efficiency, aiding healthcare professionals in monitoring and managing respiratory health.