In order to understand the meaning of pranayama, we need to first understand the meaning of prana.
What is Prana?
Prana is roughly translated as energy or vital force. From the yogic point of you, the entire cosmos is alive, throbbing with prana. Prana is ever present in every aspect of creation.
It is said in Kathopanishad (2:3:2) that :
This whole world - whatever there is - vibrates having originated from prana.
Everyone is born with a certain quantum of prana, but the quantity and quality change continuously, as we go through life.
Positive thoughts,higher feelings and yogic practises generate higher levels of prana. We can also receive prana from food, environment, sun, water and air.
However, prana is not received only from external sources. It can be self-generated. We can work with our prana to enhance life's vitality, strength, to boost capability, efficiency, to cure diseases and to develop higher states of awareness.
The aim of pranayama is to help us guide our prana whithin our energetic body.
The medium of pranayama is the breath.
The practises involve guiding the respiration beyond its normal limit, stretching it, speeding it up and slowing it down in order to experience the full range of respiration on the physical and spiritual level.
Pranayama has two etymological meanings:
1) Prana + ayama - expansion of prana
2) Prana + yama = control of prana
When we work with pranayama (breathwork), we enter into the process of expanding or stretching prana (prana + ayama) as well as we work on our ability to stop the prana (breath) to control it (prana + yama).
Both explanations convey the meaning of pranayama.
The practice of pranayama has a direct effect on the functioning of the brain.
Pranayama has the ability to blend together the different cells in the brain reducing the brainwave activity. This mean less chaos in the brain, less unorganised thoughts, feelings.