An Aiúa was an intelligent philote. Sentient creatures consisted of uncounted numbers of philotes and one Aiùa, which held the collection together and could have been thought of as the physical representation of the soul.[1]
According to Grego Ribeira, the term was inspired by the Sanskrit word for 'life,' likely "āyus."[1]
The first time aiúas were mentioned was when Ela Ribiera, Andrew Wiggin, and Miro Ribeira were trying to get to the Outside; a region outside of the universe that contained an infinite number of Aiùas.[1]
Formic Hive Queens had the ability to see Aiùas, and see how powerful or "bright" they were. The Hive Queen of Shakespeare explained that one did not have an Aiúa, one was an Aiúa, and that all creatures capable of movement were one at a fairly high level.[2]