Conceptual Art is a form of expression where the signified supersedes in importance the signifier or, in other words, where the process of creation is more important than the object created. This meta-art or anti-art originates from French artist Marcel Duchamp whose 1910s ready-mades tried to expose the inner workings of institutionalized art. His "Fountain" (1917) was actually a real urinal on which he put his signature. His "Mona Lisa" (1919) added a mustache, a beard, and an obscene riddle to the famous portrait. The removal of the sacred aura surrounding art influenced every form of expression, especially during the 1960s and after. In music, John Cage was one of the first to experiment with conceptual art with his 1954 work "4:33" -- four minutes thirty-three seconds of silence (even more conceptual was the act of releasing the piece on a record). Basically, any work in which the process of creation or the intention motivating the artist is obviously more important (to the artist and the listener) than the results it created belongs to conceptual art.
One good example is DJ Christian Marclay's Record Without Grooves (Ecart Editions, 1987), a virgin LP. The same artist also released Footsteps (Rec Rec, 1990), a one-sided LP of recorded footsteps. After being pressed, the 1000 copies were scattered on the floor of an art gallery and visitors were invited to step on them. When the LP is played, the dirt and scratches blend in with the recorded material. Such albums are usually released in very limited quantities and collected and preserved as works of art. Not all conceptual artists work with the medium itself (be it LP or CD). Some play on the definition of music. Other approaches in conceptual art include (but are by no means limited to) Christof Migone's extremely minutious studies of a very short sample (to the point of leaving only silence), Jliat's replacement of music by series of raw data, and Koji Asano's long sound art pieces packaged with as little information as possible in order to render the reality of his work more blurry.