Final answer:
The subject at hand is demography, a discipline that studies the age structure of populations to analyze population growth and infer economic development levels. Population pyramids illustrate these structures, with underdeveloped countries showing a broad base (many young people) and developed countries a more conical shape (more elderly).
Step-by-step explanation:
The question relates to the discipline of demography which is concerned with the age structure of a population and its implications for population growth and economic development. The age structure indicates the proportion of a population that falls into various age categories. This information can be represented visually using population pyramids, which provide insights into the characteristics of a population's growth. For example, countries with rapid growth typically display a pyramidal shape in their age structure diagrams, indicating a large number of young people, many of whom are of reproductive age. This pattern is associated with underdeveloped countries where life expectancy is shorter and birth rates are higher. Conversely, developed countries tend to show a more conical age structure with fewer younger individuals and a larger proportion of middle-aged and elderly individuals, reflecting lower birth rates and higher life expectancy. Thus, the age structure can serve as an indicator of the level of economic development in a given area.