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1.
the opposite of mainstream. usually not the 'trend' and usually not what everybody else is doing. original and individual. can usually be identified as something original and/or something that will probably never become popular, but awesome nevertheless.
mainstream : conformists :: non-mainstream : individuals.

SOMETIMES alternative/emo/indie music. other music, such as pop punk, can be mistaken as non-mainstream.
by ruth February 14, 2005