In fashion avant-garde refers to high concept and innovative pieces of clothing that are designed to push the boundaries of what people consider beautiful or even wearable. Though there have always been designers who have pushed the envelope, avant-garde is considered to be a modern phenomenon in so much as the word itself is used more often in modern times.
There is no strict definition for what is and is not avant-garde therefore the term can be used with broad strokes and few repercussions. Unlike more specific descriptors like haute couture and bespoke avant-garde can be used to describe any article of clothing that the designer or critic wishes to label as such. The term "avantgarde" is also often times referred to a very refined and exclusive (in terms of high-end and price) taste.