Which of the following best defines urban decay?

Urban decay refers to the process by which an urban area experiences a decline in its economic, social, and physical conditions. This decline often manifests in deteriorating infrastructure, increasing unemployment, and a rise in crime rates. A previously vibrant area may suffer from neglect, leading to vacant buildings, lower property values, and a general decrease in the quality of life for residents.

This concept is crucial in urban studies, as it highlights the challenges some city areas face in maintaining their functionality and attractiveness over time. The other choices focus on positive developments or transformations, such as rehabilitation of buildings, improvement of infrastructure, and population increases, which contrast with the negative implications of urban decay. Therefore, the definition that captures the essence of urban decay is the decline of a previously functioning city area.