In statistics, a defined group of people from which one’s sample of representative subjects are drawn.
Example: A researcher uses a representative sample (both genders, and a variety of ages, races, income levels) of 100 Americans to test the effects of a smoking cessation program. In this case, the population from which the sample is drawn would be “all Americans”.
Grinnell, R. (2009). Population. Psych Central. Retrieved on May 5, 2015, from http://psychcentral.com/encyclopedia/2009/population/