What is 'The Blue Flute' you may ask.
It is considered to be a sacred object among the Iknimayan; though it is considered a sacred spirit (very similar to Eywa). There is only one flute in exsistance and is usually kept in the Limbs of Hometree. It is serves as a guardian spirit and a concrete representation of the connection of the Navi with hometree.
The flute (actually a one-holed trumpet in terms of playing techniques) is of ancient ancestry, Navi mythology reports that Eywa plucked a branch from the Hometree, created the Blue Flute, and gave it to the Iknimaya with the intent that it be used as a device to communicate with her or the spirits of ancestors who have passed on.
The Flute is only played on the most sacred of occasions and is only played by one Navi.