Avant-garde music is a term used to characterize music which is thought to be ahead of its time, i.e. containing unique or original elements, or unexplored fusions of different genres.
Historically speaking, musicologists primarily use the term "avant-garde music" for the radical, post-1945 music after the death of Anton Webern in 1945, or "starting with Wagner" or even with Josquin Desprez.
Today the term may be used to refer to any other post-1945 tendency of modernist music not definable as experimental music, though sometimes including a type of experimental music characterized by the rejection of tonality.
Although some modernist music is also avant-garde, a distinction can be made between the two categories. Because the purpose of avant-garde music is necessarily political, social, and cultural critique, so that it challenges social and artistic values by provoking or goading audiences, composers such as Richard Strauss, Arnold Schoenberg, Anton Webern, George Antheil, and Igor Stravinsky may reasonably be considered to have been avant-gardists in their early works (which were understood as provocative, whether or not the composers intended them that way), but the label is not really appropriate for their later music.