Post-Metal

This heavy metal movement takes influences from post-rock. While it is in many ways similar to post-rock, post-metal tends to include lower-tuned guitars, distorted guitar(s), heavy atmospherics, gradual evolution of song structure, and a minimal emphasis on vocals. Post-metal stresses emotion, contrasting the ambiance of post-rock with the weight and bombast of metal. Vocals are deemphasized or non-existent, and lyrics tend to be equally abstract: often thematic or philosophical in nature. It is a largely American phenomenon, but also includes some Japanese bands. Bands like Neurosis, Isis, Cult of Luna and Pelican write lengthy songs (typically five or six per album) that can range from light and guitar-driven to heavy, drum and bass-driven.

Source: http://en.wikipedia.org/wiki/Post-metal