Prana is the life-force. Breath is its most accessible face — and Pranayama is its direct cultivation — but prana in the yogic picture is more than breath. It flows through subtle channels (nadis) and gathers at energetic centers (chakras); its free movement is health, its blockage is dis-ease.
The concept has close cousins across Asian traditions: Chinese chi (or qi), Japanese ki, Tibetan lung. All describe a subtle animating energy that can be cultivated, blocked, or dispersed.
Modern biomedicine has no direct equivalent; contemporary evidence-based readings of prana typically reinterpret it as nervous-system and respiratory physiology. The traditional frame holds that something not captured by those categories is still in play.