Let’s explore the Sanskrit word pranayama. Prana is our life force energy, and pranayama includes various ways of working with the breath to affect change in our prana. Leslie Kaminoff calls it the practice of “unobstructing the breath,” or removing any obstacles that might be preventing it from being slow and subtle (see Yogasutra 2.49-2.53 for what how the ancients described it).
Using various practices to work with the inhale, exhale, pauses between (and bandhas, or locks) guides the system towards a state of balance. James Nestor made the breath popular with his book Breath, but yogis have been fine tuning the subtleties of pranayama for thousands of years.