It means that the MP3's have been recorded at 320KBPS, which is the highest and best quality for an MP3. This could apply to any sort of music, but with dubstep when that number starts to decrease, so does the quality and impact of the bass and other parts of the track. The 320 is not a specific reference to dubstep, just how good the MP3 is.
"Yo, can I get a 320 of that sick track?
by Crazy Killalette July 09, 2010
3 more definitions
The time at which students find themselves texting after school.
I find myself texting at '320' (3:20) every day after school.
by Narhen September 20, 2011
the greatest time
It's a motherfucking celebration
by Everett Webre February 17, 2009
Secret underground oranization consisting of its original members N.E.R.D,portis, deuce, billie joe(aka little t but that was a long time ago) and gorrillaz
we 320ed them. they make me use up 20 letters in this example
by 320ers June 04, 2005