Challenges with Terminology Throughout this review, we compiled a glossary of common terms, including the following: urban, slum, urban population, urban poor, city, town, slum-like settlement, slum household, informal settlement, informal sector, informal work, informality, and squatter settlement. It became apparent that there is no global consensus on the definitions of key terms; often the key terms – such as “urban” or “poor” – are not defined at all. This makes most comparisons across cities, countries, and trends over time impossible to state with certainty. In fact, it makes most of the quantitative data in the literature unreliable [9, 20]. For that reason, no paper or other evidence was excluded from consideration because it failed to meet a particular definition of “slum” or “urban poor.” In the text, we use “slum” and “informal settlement” interchangeably and vacillate between “slum” and “urban poor” depending on whether we are talking about the place or the people. This is done to reflect the way that these terms are usually used by the literature and by our informants.