Symphonic Metal

Symphonic metal varies in form. It most commonly refers to heavy metal bands that use orchestral elements in their music. These elements include full orchestras, opera themes, vocals or keyboard playing akin to that of opera or symphony music, and a softer and more upbeat nature than other metal genres. Prominent examples include Therion, Nightwish, Within Temptation, and Epica. Although many symphonic metal bands base their style solidly on classical music, a few follow a theatrical, more epic approach to this genre by including or basing their style in Film Music or movie soundtracks. Keyboards are normally the focal point of the music. While other instruments typically play relatively simple parts, the keyboard parts can be very complex and technically challenging, often played in a wide variety of classical styles and emulating anything up to and including full orchestral arrangements. An actual orchestra is sometimes employed, both live and in the studio, to similar effect.

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