Demography is the study of the characteristics of a population as well as groups within a population.
The word "demography" comes from a combination of two Greek words:
DEMOS (δῆμος) meaning "the people" and GRAPHE (γραφη) meaning "writing."
So, "demography" is "writing about the people."
And "demographics" are the statistical data on the characteristics of a population and/or particular groups within it. In other words, demographics are the numerical outputs resulting from the study of a population.