Diaphragm is the dome-shaped muscle beneath the lungs that does most of the work of breathing.
On an inhale it drops and the lower ribs widen; on an exhale it rises. When it is free, the belly and the sides move. When it is held, the chest and shoulders take over and the breath stays high. In 📝Breathwork the diaphragm is the engine being invited back online, not a diagnosis of a hernia or of a medical breathing disorder. The word in a session note locates the muscle, not a lesion.
Clients feel it as a belly that can move, or as a ribcage that will not widen. Practice is slow nasal inhales that let the lower ribs go sideways, not a contest of how big the breath can get. Chest pain, unexplained shortness of breath, or dizziness is a stop and, if it persists, a referral.