a) The description of a melodic/rhythmic track (mostly electronic) that has a sense of euphoria associated to it.
b) A corruption of the word tune used in an adjectival form.
c) An almost generic description for an uplifting house/trance track.
"Dude, check this track out. It's soooo freakin' choonsie."
"OMG! That's like THE choonsiest track I've ever heard."
"At the moment I'm listening to 'Orbital - Belfast'. Now tell me that that's not choonsie?"
"I've got the urge to dance. I think I'll go put on a nice choonsie track."