Used as an alternative to old school. Refers to old fashioned/retro methods, ways and style. Often a comparison with the trends and fashion of today.
In Cee Lo Green's song 'Fuck You':

Yeah, I'm sorry, I can't afford a Ferrari,
But that don't mean I can't get you there.
I guess he's an X-box and I'm more Atari,
But the way you play your game ain't fair.

X-box refers to 'today's'/modern style, while more Atari refers to old fashioned/'yesterday's' style...
by SEYDLITZ January 15, 2013
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