The term has traditionally referred to housing areas that were once respectable but which deteriorated as the original dwellers moved on to newer and better parts of the city, but has come to include the vast informal settlements found in cities in the developing world.
Many shack dwellers vigorously oppose the description of their communities as 'slums' arguing that this results in them being pathologised and then, often, subject to threats of evictions. Many academics have vigorously criticized UN-Habitat and the World Bank arguing that their 'Cities Without Slums' Campaign has led directly to a massive increase in forced evictions.
Although their characteristics vary between geographic regions, they are usually inhabited by the very poor or socially disadvantaged. Slum buildings vary from simple shacks to permanent and well-maintained structures. Most slums lack clean water, electricity, sanitation and other basic services
"Slum" was originally used mainly in the phrase "back slum," meaning a back room and later "back alley," . The Oxford English Dictionary says it may be a "cant" word of Roma (Gypsy) origin. The etymologist Eric Partridge says flatly that it is "of unknown origin."
Other terms that are often used interchangeably with "slum" include shanty town, favela, skid row, barrio, ghetto, and "The Hood," although each of these has somewhat different meaning. Slums are distinguished from shanty towns and favelas in that the latter initially are low-class settlements, whereas slums are generally constructed early on as respectable, often prestigious communities. Skid row refers to an urban area with a high homeless population. The term is most commonly used on the west coast of the United States. Barrio may refer to an upper-class area in some Spanish-speaking countries, and only is used to describe a low-class community in the United States. Ghetto refers to a neighbourhood based on shared ethnicity. By contrast, identification of an area as a slum is based solely on socio-economic criteria, not on racial, ethnic, or religious criteria. The term "The Hood" is used in the United States only to describe a slum with a high African-American population.
The characteristics associated with slums vary from place to place. Slums are usually characterized by urban decay, high rates of poverty, and unemployment. They are commonly seen as "breeding grounds" for social problems such as crime, drug addiction, alcoholism, high rates of mental illness, and suicide. In many poor countries they exhibit high rates of disease due to unsanitary conditions, malnutrition, and lack of basic health care. A UN Expert Group has created an operational definition of a slum as an area that combines to various extents the following characteristics: inadequate access to safe water; inadequate access to sanitation and other infrastructure; poor structural quality of housing; overcrowding; and insecure residential status. To these one might add the low socioeconomic status of its residents.
In many slums, especially in poor countries, many live in very narrow alleys that do not allow vehicles (like ambulances and fire trucks) to pass. The lack of services such as routine garbage collection allows rubbish to accumulate in huge quantities. The lack of infrastructure is caused by the informal nature of settlement and no planning for the poor by government officials. Additionally, informal settlements often face the brunt of natural and man-made disasters, such as landslides, as well as earthquakes and tropical storms. Fires are often a serious problem.
Many slum dwellers employ themselves in the informal economy. This can include street vending, drug dealing, domestic work, and prostitution. In some slums people even recycle trash of different kinds (from household garbage to electronics) for a living - selling either the odd usable goods or stripping broken goods for parts or raw materials.
Slums are often associated with Victorian Britain, particularly in industrial, northern towns. These were generally still inhabited until the 1940s, when the government started slum clearance and built new council houses. There are still many examples left of former slum housing in the UK, however they have generally been restored into more modern housing.
Recent years have seen a dramatic growth in the number of slums as urban populations have increased in the Third World. According to a 2006 UN-HABITAT report, 327 million people live in slums in Commonwealth countries - almost one in six Commonwealth citizens. In a quarter of Commonwealth countries (11 African, 2 Asian and 1 Pacific), more than two out of three urban dwellers live in slums and many of these countries are urbanising rapidly.
Many governments around the world have attempted to solve the problems of slums by clearing away old decrepit housing and replacing it with modern housing with much better sanitation. The displacement of slums is aided by the fact that many are squatter settlements whose property rights are not recognized by the state. This process is especially common in the Third World. Slum clearance often takes the form of eminent domain and urban renewal projects, and often the former residents are not welcome in the renewed housing. Moreover new projects are often on the semi-rural peripheries of cities far from opportunities for generating livelihoods as well as schools, clinics etc. At times this has resulted in large movements of inner city slum dwellers militantly opposing relocation to formal housing on the outskirts of cities. See, for example, Abahlali baseMjondolo in Durban, South Africa.
In some countries, leaders have addressed this situation by rescuing rural property rights to support traditional sustainable agriculture, however this solution has met with open hostility from capitalists and corporations. It also tends to be relatively unpopular with the slum communities themselves, as it involves moving out of the city back into the countryside, a reverse of the rural-urban migration that originally brought many of them into the city.
Critics argue that slum clearances tend to ignore the social problems that cause slums and simply redistribute poverty to less valuable real estate. Where communities have been moved out of slum areas to newer housing, social cohesion may be lost. If the original community is moved back into newer housing after it has been built in the same location, residents of the new housing face the same problems of poverty and powerlessness. There is a growing movement to demand a global ban of 'slum clearance programmes' and other forms of mass evictions.