You may have heard choir directors and voice teachers say "breathe with your diaphragm," but most people don't really know
where their diaphragm is or how it works.
The diaphragm is a thin skeletal muscle that sits at the base of the chest and separates the abdomen from the chest. It contracts and flattens when you inhale. This creates a vacuum effect that pulls air into the lungs. When you exhale, the diaphragm relaxes and the air is pushed out of lungs.
When singing teachers tell you to breathe with your diaphragm, what they mean is to feel the movement of breathing low in your abdomen rather than high in your chest.