What does population structure mean?

Structure refers to 'shape' of population. The population is divided into groups by age ('cohorts'). These might be 0-5 year olds, 46-50 year olds etc... Typically they are displayed on a population pyramid.

The percentage of the total population is worked out & placed within these age categories. The structure then describes the shape of these groups within the population.

A young population will have a high Birth Rate & a large percentage of young people.

An ageing population will have a larger percentage of older people, low birth rate & high life expectancy.