Has anyone nailed down the origin of this term? My off-the-cuff guess is that it mimics the theme from The Twilight Zone.
Used how? I’ve heard people make this noise, mostly as an exclamation (or imitating a train whistle), but I don’t think I could ascribe a consistent meaning to it.
The OED2 has
Imitative of the sound of wind.
1841 CARLYLE Misc. Ess., Baillie (1872) VI. 215 The ever~moaning..unsyllabled woo-woo of wind in empty churches!
I think the poster means woo-woo as meaning eerie, otherworldly, mysterious, etc.
“I tried reading that book, but it was a little too woo-woo for my taste.”
It’s also been used to mean steeped in New Age nonsense. Used commonly on Randi’s site http://www.randi.org/site/
I made a half-hearted effort to track it down, but quickly ran into the problem of too many false positive hits.
I’m still meaning to make a concerted effort on the term.