Banlieue
Banlieue is the French word for suburb. A banlieue can be rich or poor: as an example, Versailles, Le Vésinet, and Neuilly-sur-Seine are affluent banlieues of Paris, and Clichy-sous-Bois is a poor one. The literal meaning of the word is ban-mile (ban-league), originally a zone surrounding a city where no unauthorized trade was permitted.
Euphemism
However, since the 1970s and 1980s, the word has also been increasingly used as a euphemism to describe low-income housing projects in which mainly foreign immigrants reside, especially around Paris, but also some large French cities.
Since the 1980s petty crime has increased in France, much of it blamed on juvenile delinquency. As a result the banlieues are perceived to have become rather unsafe places to live, and youths from the banlieues are perceived to be one important source of increased petty crimes and uncivic behaviour. As a result of this criminality, the National Front, a far right political party led by Jean-Marie Le Pen, rose to prominence during the early 1990s on an platform of tougher law enforcement and immigration control.
The French phrase langue de la banlieue, literally "language of the suburb," is a euphemism for the forms of slang currently used by banlieue youth, or people emulating them. Typically this refers to verlan.
A modern translation of banlieue from French to English is "Ghetto". To some extent, French banlieues resemble US "black ghettos": high criminality, drug trafficking, and rap music.
Note that this connotation of the word is mostly restricted to European French. In Quebec and Africa, the word retains its neutral meaning.
Violent clashes between hundreds of youths and the French Police in the Paris banlieue of Clichy-sous-Bois began on October 27th, 2005 and have continued for 8 consecutive nights. The 2005 Paris suburb riots were triggered by the electrocution deaths of two teenagers who were attempting to hide from police in an electricity substation.
Banlieues rouges
The banlieues rouges ("red suburbs") are suburbs of Paris where, traditionally, the French Communist Party held mayorships and other elected positions (Ivry-sur-Seine, Châtillon...). As an example, such suburbs would have some streets named after Communist personalities, such as rue Youri Gagarine.