A demographic is a subset of a population that shares a common factor such as age, income or education level.
The millennial generation, for example, is the demographic cohort that immediately follows Generation X. Although there is a great deal of variation from one individual to another within any generational cohort, the particular environment for any generation affects those individuals in ways that are observable as broad tendencies.
Insight into those tendencies and other characteristics of various demographics can inform research and analysis in many areas, including business intelligence (BI), customer relationship management (CRM), marketing, recruitment, policy development, economics, psychology and healthcare.
The word demographics comes from the Greek words dēmos, meaning "the people" and -graphy which is associated with the acts of writing, description or measurement.