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.

A man who messes around with other men, but no one would ever know by looking or talking to him. Used by gay black men to identify masculine gay men or DL Brothas.

16th November (320th day of the year) 1996 - Birth of the Psychedelic Princess

The time at which students find themselves texting after school.

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