Definition of "sludge"

sludge

/slʌd͡ʒ/

noun
countable and uncountable, plural sludges
1. Solids separated from suspension in a liquid.
  Quotations
  Floods in northern India, mostly in the small state of Uttarakhand, have wrought disaster on an enormous scale. […] Rock-filled torrents smashed vehicles and homes, burying victims under rubble and sludge.
  2013 June 29, “High and wet”, in The Economist, volume 407, number 8842, page 28
2. A residual semi-solid material left from industrial, water treatment, or wastewater treatment processes.
3. A sediment of accumulated minerals in a steam boiler.
4. A mass of small pieces of ice on the surface of a water body.
5. (uncountable, music) sludge metal
verb
third-person singular simple present sludges, present participle sludging, simple past and past participle sludged
1. (intransitive, informal) To slump or slouch.
2. (intransitive) To slop or drip slowly.