Experimental music

Experimental music refers, in the English-language literature, to a compositional tradition which arose in the mid-twentieth century, particularly in North America, and whose most famous and influential exponent was John Cage (Grant 2003, 174). More loosely, the term is used to describe music within specific genres that pushes against their boundaries or definitions, or else whose approach is a hybrid of disparate styles, or incorporates unorthodox, new, distinctly unique ingredients (Anon. [n.d.]a).

Source : http://en.wikipedia.org/wiki/Experimental_music