original and unusual, innovative and experimental, referring to ideas, techniques, or people favoring these;
e.g. It is not unusual for avant-garde art to cause some controversy or outrage.
(noun)
the group of intellectuals, especially in an artistic field, who favor or introduce original and unusual ideas and experimental/innovative concepts, or the ideas and concepts thus introduced;
e.g. This technique was developed by the avant-garde of the sculpture world at the time