Simply said, Pranayama is the Indian Yogic practice of conscious breath control, an ancient type of breathing exercise, which today is usually called Breathwork. Mind that the phrase Pranayama is a general term for a range of different Pranayamas.
Moreover, throughout the centuries Pranayama practices have seen significant changes in the way they are applied, and even today it depends very much on the goal and type or lineage of Yoga how Pranayama is used.
For instance, they can be applied as synchronization of the breath during or between Yoga postures (Asanas) and movements. The may be used to purify and cleanse the Yoga Nadis, or alternatively they can be practiced as an exercise on its own, before or after Yoga exercises, at any moment of the day, or within Tantric Sex.
The word Pranayama is generally considered to be a conjunction of the words Prana and Ayama, where Prana means “breath” or “air,” and Ayama is translated in a variety of ways, such as “suspension,” “expansion,” “restrain,” and “control,” among other interpretations.
In ancient Hindu, Yogic, and Tantric texts, the goal of doing Pranayama is to get into a trance-like state by stopping all breathing with an aim of detachment, activation of the Sushumna Nadi and Kundalini Energy, liberation of bondage, and finally Spiritual Enlightenment.
The Yoga Sutras of Patanjali, an influential Yoga text, essentially considers Pranayama exercises as a means to acquire deep concentration, subsequently followed by meditation, with the ultimate goal of attaining spiritual enlightenment.
In Hatha Yoga various Pranayama techniques are used, for instance, between movements, or in so-called Bandhas and Mudras. They are applied to attain higher spiritual or awareness levels, controlling and directing Life Energy (Prana) for several aims, or as a means of therapeutic healing, among other applications.
Today, in mainstream health and bodywork practices, Pranayama is used for stress relief, as a means of mindfulness, better concentration and improved cognitive performance, better sleep and a lower blood pressure, to name some of the more common contemporary down-to-earth applications.