Prāṇāyāma is the extension or control of the vital breath. In the Yoga Sūtras it follows posture and steadies the mind by slowing and regulating the breath. Haṭha yoga developed many techniques, including retention, and linked breath to the movement of energy in subtle channels.
Prāṇāyāma
Regulation of the breath: the fourth limb of yoga, controlling inhalation, exhalation and retention.
Also: Pranayama