urban settlements or neighbourhoods that developed outside the formal system that is meant to record land ownership and tenure and without meeting a range of regulations relating to planning and land use, built structures and health and safety. Informality is a broader concept than 'slums', which are usually defined using measures of housing quality, provision of services and overcrowding. While most countries do not generate formal statistics on the number of people living in informal settlements, UN Habitat provides regional and global estimates of the number of urban households that are 'slum' households and therefore likely to include most residents of informal settlements. These estimates suggest that there were 1034 million slum dwellers in 2018, including some 56% of the urban population in sub-Saharan Africa and more than 30% of the urban population of South Asia . Informality is particularly important in understanding climate risks and responses in cities and settlements, and also in relation to key infrastructure .
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report