Population Density: This refers to the number of individuals per unit area or volume. It's like counting the number of people living in each apartment building in our city analogy.
Carrying Capacity: This is the maximum population size that an environment can sustain indefinitely. It's similar to knowing how many people can comfortably live in our imaginary city without exhausting resources.
Demography: The statistical study of populations, especially human beings. In our city analogy, this would be like studying who lives in the city - their ages, occupations, etc.