What is "sludge metal"

n. An abrasive, distorted subgenre of heavy metal music influenced by punk and grunge.

Sludge metal (sometimes referred to simply as "sludge") is an extreme genre of music that melds elements of doom metal and hardcore punk, and sometimes Southern rock. Sludge metal is typically harsh and abrasive, often featuring shouted or screamed vocals, heavily distorted instruments and sharply contrasting tempos. While the style was anticipated by the Melvins from Washington, many of its earliest pioneers were from the city of New Orleans.