Before defining Pranayama, it is necessary to understand prana.
Prana is not merely breath. It is not oxygen. It is not a symbolic metaphor. In the Vedic vision, prana is the animating principle of life. It is the subtle force that sustains movement, perception, digestion, circulation, and thought.
In the Prashna Upanishad, prana is described as the chief vital force among all functions of the body. The text narrates how the organs once argued about their superiority, until prana prepared to depart. As prana withdrew, all other faculties weakened. When prana returned, they regained strength. The teaching is clear. Prana is foundational.
The Upanishad declares that prana sustains both body and mind. It is not subordinate to thought. Rather, thought depends upon it.
Therefore, when the tradition speaks of regulating breath, it is not merely manipulating air. It is disciplining the flow of life-force.