In demography, the age pyramid is a graphical representation of the distribution of the population (horizontal axis) of a region by age (vertical axis) and sex (men on the left, women on the right). The term pyramid is used because in a population in which there are more young people than elderly, the graph gradually takes on a pyramidal shape.
The form of the pyramid, however, can change when birth, death and migration conditions change. For example, in France at present where the population is ageing, the graph is no longer pyramidal but looks more like a mushroom.
The age pyramid has changed greatly in France over the last century. © Insee