Pranayama is the art of breathing.
More specifically, to the Expansion of Breath or Pranic Sheath Pranamayakosha the 2nd of the 5 coverings according to the Kosha Model.
Nadi Shodanham belongs to the class of exercises known as pranayama.
Aleister Crowley had his version of what he thought pranayama was:
Chapter 4 of Crowley's Eight Lectures on Yoga
Related: Aleister Crowley