The noun population has 5 senses (first 4 from tagged texts)
1. (27) population -- (the people who inhabit a territory or state; "the population seemed to be well fed and clothed")
2. (4) population -- (a group of organisms of the same species populating a given area; "they hired hunters to keep down the deer population")
3. (3) population, universe -- ((statistics) the entire aggregation of items from which samples can be drawn; "it is an estimate of the mean of the population")
4. (1) population -- (the number of inhabitants (either the total number or the number of a particular race or class) in a given place (country or city etc.); "people come and go, but the population of this town has remained approximately constant for the past decade"; "the African-American population of Salt Lake City has been increasing")
5. population -- (the act of populating (causing to live in a place); "he deplored the population of colonies with convicted criminals")