The correct answer is - population.
The population is defined as the total number of people inhabiting a country, region, city, district. In the simplest possible way the population can be seen as a purely statistical number, but if we go deeper into it, the population has lots of other aspects apart from the number itself.
A population can further be studied by its age, education, race, ethnicity, sex representation, languages spoken etc, and they all as a whole give us a better picture about the structure of a population.