Drone music, drone-based music, or simply drone, is a minimalist genre that emphasizes the use of sustained sounds, notes, or tone clusters – called drones. It is typically characterized by lengthy audio programs with relatively slight harmonic variations throughout each piece. La Monte Young, one of its 1960s originators, defined it in 2000 as "the sustained tone branch of minimalism".

The modern genre also called drone music (called "dronology" by some books, labels and stores, to differentiate it from ethnic drone-based music) is often applied to artists who have allied themselves closely with underground music and the post-rock or experimental music genres. Drone music also fits into the genres of found sound, minimalist music, dark ambient, drone doom/drone metal, noise music and ambient.

from Wikipedia