(n) the act of air being received into and expired from the lung

Q why do we need to do breathing exercises?
A. To ensure we have a steady tone & to regulate how we use our breath.
Breathing exercises help to relax the body and slow down the heart rate. Oxygen feeds the body and brain, so the better we utilize our intake, the more efficiently we function. Breathing exercises have been used for thousands of years in relaxation techniques and meditation, both of which help relax tense muscles and focus mind, body and spirit on a given task. So, we do need to exercise our breathing and its importance should not be overlooked.
Relaxing the muscles in our larynx and pharynx is necessary if we are to vocalize freely, it is impossible to sing when they are tense.
Breathing exercises not only improve our respiratory reflexes, but provide a controlled flow of air. When we speak hum or sing the air passes our vocal folds (or vocal chords), they vibrate and create the sound.
The diaphragm supports the breath and breathing exercises strengthen the diaphragm both of which are energized and supported from the pelvic floor.
As we breathe in we push down our abdominal muscles and visualise filling our lungs slowly from the bottom first through to the top last.
As we breathe out, we pull up through the body, first from the pelvic floor then through the lower abdominals slowly releasing our breath as we pull inward and upward. At this point we are fully supported then as we continue to breathe out we visualise our lungs emptying from the bottom first to the top last. Our shoulders should be nice and relaxed at all times.