1. not part of or conforming to the dominant or widely accepted ideas, practices, or culture

Examples

• The film festival featured many nonmainstream movies from independent directors.
• Her nonmainstream approach to teaching attracted both praise and criticism.
• The band’s nonmainstream sound appealed to a small but devoted following.
• Nonmainstream political parties often struggle to gain widespread support.
• The artist’s nonmainstream style challenged traditional artistic conventions.
• Many nonmainstream religions have gained followers in recent decades.