‘אוירא דכיא’ ‘Pure air’ is the chassed of Atik (supernal Keter) of the ‘skull. It is called pure because it has no Tzimtzum
‘Air’ represents the light of Ruach that is the six sefirot of Z”A, and Chessed of Atik that is dressed in the skull of Arich Anpin.
To simplify the meaning of ‘אוירא דכיא’ ‘Pure Air’ consider it as Chassadim of Arich Anpin.
Synonyms:
Pure air