The names, in yoga terminology, I am never put randomly, and often hide the effects of a practice, or the right attitude to practice, the different levels on which it works, or even a symbolism that clarifies where practice really wants to take.
If we narrow the field and understand that Pranayama is based primarily on listening techniques and the manipulation of breath (the main mode of supply of vital energy, The path of prana), we see that the term Pranayama simply means restriction of breathing.
This may seem a little strange, if you think these yogis who claim to be able to extend at will the life and furthermore it can be done by restricting a vital function as important as the breath that we have the feeling of wanting to expand as much as possible.
We are used, even from a yogic culture interpreted in a superficial and incorrect, to think that you just do some deep breaths and take as much oxygen as possible and eliminate the "harmful" carbon dioxide.
The yogis tell us exactly the opposite, to breathe a little, slowly, so silent and imperceptible, even they tell us that we have available, at birth, not a number of years but a number of breaths, then, to use very sparingly ....! And the mouth is made not only to eat and talk but also to be silent, closed and to breathe the nose and belly ...