The definition of demographics

The characteristics and statistical information
that distinguish a group of people. These
characteristics commonly include age, gender,
ethnicity, occupation, interests and other
quantifiable criteria. A business’ target
demographic captures the group of people at
which their products or services are aimed.
Advertisements created through ad platforms
such as Facebook, AdSense and AdWords usually
allow for you to specify certain demographic
information so that your ad targets the
interested people.
(http://www.hudsonhorizons.com)