4'33"

From wikipedia:

4′33″ (pronounced "Four minutes, thirty-three seconds") is a three-movement composition by American experimental composer John Cage (1912–1992). It was composed in 1952 for any instrument (or combination of instruments), and the score instructs the performer not to play the instrument during the entire duration of the piece throughout the three movements (which, for the first performance, were divided into thirty seconds for the first, two minutes and twenty-three seconds for the second, and the third being one minute and forty seconds). The piece purports to consist of the sounds of the environment that the listeners hear while it is performed, although it is commonly perceived as "four minutes thirty-three seconds of silence".