What does the term "urbanization" refer to?

The term "urbanization" specifically refers to the process by which an increasing percentage of a population comes to live in urban areas, leading to a concentration of people in cities and towns. This trend is often driven by various factors, including economic opportunities, employment prospects, better access to services and amenities, and the pursuit of a higher quality of life. As more individuals migrate from rural areas to urban centers, these areas tend to experience growth in both size and population density, which can result in significant changes to local economies, social structures, and cultural dynamics.

The other options do not adequately capture the essence of urbanization. The migration of people to rural areas would be the opposite of urbanization, representing a trend toward de-urbanization. A decline in the population of urban regions implies a decrease in urbanization, rather than an increase. The construction of rural infrastructure relates more to development in non-urban areas and does not reflect the phenomenon of increasing urban population density. Thus, the correct answer encapsulates the core idea of urbanization as the concentration of population in urban areas.