From Destinypedia, the Destiny wiki

Aivanti-3 was an AI created and trained during the Golden Age. It was capable of composing music, such as "Siegfried in the Storm Wall".[1]

The suffix "-3" denoted that it was the third version or iteration of the Aivanti AI trained, having been preceded by Aivanti-1 and Aivanti-2. Citing Aivanti as inspiration, Clovis Bray I adopted the same system for Exo names, in his case to designate the number of times a given Exo had been rebooted.[2]