What is the process of breathing out called?

The process of breathing out is known as exhalation, which specifically refers to the act of expelling air from the lungs. During exhalation, the diaphragm and intercostal muscles relax, causing the chest cavity to decrease in volume, which increases the pressure inside the lungs. This higher pressure forces air out of the lungs and into the atmosphere.

Other terms associated with respiration highlight different aspects of the breathing process. Inspiration refers to the act of inhaling air into the lungs, while respiration generally encompasses the broader process of gas exchange, including both inhalation and exhalation. Ventilation refers to the movement of air into and out of the lungs but does not specifically denote the act of breathing out. These distinctions clarify why exhalation is the most accurate term for the action described in the question.