Population is a term from statistics and empiricism. It refers to all persons, things or cases that are investigated for a specific question or several specific questions. Because a population is often very large, for example when the opinion of the general population on a certain topic is to be found, it is often reduced to a sample for reasons of time, organization and financial resources.
The answers of the people selected for this sample are then extrapolated to the population. In order not to falsify the result, it is therefore important that the sample is representative of the population.