What does a population mean?
Population
In biology, a population is the number of all the organisms of the same group or species, which live in a particular geographical area, and have the capability of interbreeding. The area of a sexual population is the area where inter-breeding is potentially possible between any pair within the area, and where the probability of interbreeding is greater than the probability of cross-breeding with individuals from other areas.
Threshold population
In geography, a threshold population is the minimum number of people necessary before a particular good or service can be provided in an area. The concept is equivalent to the "range" in central place theory and retailing, which delineates the market area of a central place for a particular good or service, and is dependent on the spatial distribution of population and the willingness of consumers to travel a given distance to purchase particular goods or services.