"September" (Earth, Wind & Fire)

Like so many other Earth, Wind & Fire songs, "September" (first released on 1978's The Best of Earth, Wind & Fire, Vol. 1) bursts with positivity and light.  It is the kind of song that, no matter what age you are and no matter what the event (picnic, wedding, birthday, reunion, bar mitzvah, etc.), it's going to get you up and dancing.  It's impossible to sit still or be cynical when you hear that signature EW&F interplay of rhythm and melody.  (Side note: Verdine White's bassline is a masterpiece in and of itself.  Isolate it and take a listen sometime.)
Thing is, in all of the years I've been a fan of the song (and we're talking since I was running around in Pampers), I've never really known what bandleader Maurice White is singing about.  The track always had an air of nostalgia about it, what with that opening line Do you remember?  But it wasn't clear if he's reminiscing about a senior prom, a night on the town, a couple's first time, or something else entirely.
And if there's one line that has always eluded me, it's what Philip Bailey sings at the top of the chorus.  Is it party on?  Party up?  Party, y'all?  On and on?  
Turns out the line is Ba-dee-ya.  
So what does it mean?
In my own best estimate, it's onomatopoeia that mimics the sound of horns.  
One of the track's writers, the awesomely eccentric Allee Willis, recently told NPR it was a Maurice White-ism that was there just as a placeholder.  Willis (who'd been a copywriter at Columbia Records, writing liner notes for R&B albums, before singer Patti LaBelle gave her her first break as a songwriter, which led to the gig with EW&F) says that they still hadn't replaced the lyric when it came time to lay down the final vocals.  But when she begged him to change it to something other than nonsensical syllables, he convinced her that the line was perfect and memorable, as is.
"I learned my greatest lesson ever in songwriting from him, which was never let the lyric get in the way of the groove."

So I guess the moral of the story is not to get too hung up on what the song is about.  It's about whatever memories, feelings, or thoughts it conjures for you.