Exhalation refers to the act of breathing out or expelling air from the lungs. It is the opposite of inhalation, which involves drawing in fresh air into the body through the nose and mouth. During exhalation, the diaphragm muscle contracts and moves downward, while the intercostal muscles between the ribs relax, causing the chest cavity to decrease in pressure. This forces the air out of the lungs and back into the atmosphere. Exhalation is an essential part of respiration as it helps to remove waste gases such as carbon dioxide from the body, allowing for fresh oxygen to be taken in during inhalation.