What does windsong mean?

Although "windsong" is a word that I have seen used on many occasions, virtually no dictionaries list it as an accepted word. Below are a list of uses for the word.

• "Windsong" is the name of a 1975 John Denver album.


• "Windsong" was a British folk-rock band that included future star Annie Lennox (THE EURYTHMICS).


• "Windsong" was a British record label during the 1990s.


• "Mountain Windsong" is a novel about the American Indian's "Trail of Tears" saga.

I believe it is also a word that signifies the musical sound that the wind makes, although this is not an official definition.