A subgenre of metal incorporating elements from progressive rock
. The earliest bands to fuse these two genres together were Dream Theater
, Watchtower, Psychotic Waltz, and Fates Warning. (Although some argue King Crimson were ahead of their time doing this with 21st Century Schizoid Man.)
Keyboards/synths, and other instruments not seen as often in the metal genre are more commonly used in progressive metal.
It's common for progressive metal acts to have very long song lengths with plenty of complex instrumental sections which give the musicians a lot of room to show off. Odd-time signatures are also are commonly implemented.
Progressive metal lyrics tend to be very cerebral, with elements of fantasy, psychology, and science fiction thrown into the mix. (The sort of lyrics you'd expect from Stephen Hawking or Sigmund Freud if they ever formed a heavy metal band.)
, Psychotic Waltz, Fates Warning, Watchtower, Galactic Cowboys, Kings X, Spiral Architect, Symphony X, Andromeda, Shadow Gallery, Ayreon, Green Carnation, Winds, Liquid Tension Experiment, Superior, The Gathering circa-Mandylion