If you mean what is A slum; this is also referred to as a shanty towns. The web definination for this;
Shanty towns (also called slums, squatter settlements camps, favelas or Georgie Slums) are settlements (sometimes illegal or unauthorized) of impoverished people who live in improvised dwellings made from scrap materials-often plywood, corrugated metal, and sheets of plastic.
HOPE THIS HELPED !
To be in a dark place