Like it's counterpart doom,
sludge is another genre of "music" inspired by
Black Sabbath. Unlike doom however, which emphasizes slower tempos and dynamic heavy riffs.
Sludge emphasizes even slower tempos,
repetition and progression.
The Melvins, Godflesh, Boris, Buzzov-en, Isis,
Sunn 0))), and
Khanate are all excellent sludge bands.