What is the meaning of Sludge?

Solids separated from suspension in a liquid.

A residual semi-solid material left from industrial, water treatment, or wastewater treatment processes.

A sediment of accumulated minerals in a steam boiler.

A mass of small pieces of ice on the surface of a water body.

Ellipsis of sludge metal.

To slump or slouch.

To slop or drip slowly.

Source: wiktionary.org