In pranayama, the breath is treated as the most direct handle a practitioner has on prana, the current of vital energy that Hindu and yogic sources hold to animate body and mind alike. The Yoga Sutras describe pranayama simply as the regulation of the incoming and outgoing breath, undertaken once a steady posture has been established, and treat it as a preparation for withdrawing the senses and turning attention inward.
The hatha yoga texts go much further, naming a whole family of methods, distinguished by ratio, rhythm and the use of retention, and pairing them with physical locks applied at the throat, abdomen and pelvic floor. These sources describe pranayama's aims as calming the mind, purifying the subtle channels believed to carry prana through the body, and preparing the ground for the awakening of a latent energy at the base of the spine. They are equally clear, however, that the more advanced methods, particularly prolonged breath retention, are not to be attempted without a foundation in posture and without a teacher's supervision, and that improper practice can unbalance the body's constitution or cause real harm. For that reason this entry describes what pranayama is for and what tradition claims about it, rather than any sequence, ratio or count a reader could attempt unsupervised; the texts themselves reserve that instruction for direct transmission.