Breathing is the process that takes oxygen in and carbon dioxide in and then out of the body. Aerobic organisms require oxygen to release energy via respiration, in the form of the metabolism of energy-rich molecules such as glucose. The medical term for normal relaxed breathing is eupnea.
Breathing is only part of the processes that deliver oxygen to where it is needed in the body and remove carbon dioxide. The process of gas exchange occurs in the alveoli by passive diffusion of gases between the alveolar gas and the blood passing by in the lung capillaries. Once these dissolved gases are in the blood, the heart powers their flow around the body (via the circulatory system).
In addition to removing carbon dioxide, breathing results in loss of water from the body. Exhaled air has a relative humidity of 100% because of water diffusing across the moist surface of breathing passages and alveoli.