The Collaborative International Dictionary of English v.0.48:

Population \Pop`u*la"tion\, n. [L. populatio: cf. F.
   population.]
   1. The act or process of populating; multiplication of
      inhabitants.
      [1913 Webster]

   2. The whole number of people, or inhabitants, in a country,
      or portion of a country; as, a population of ten millions.
      [1913 Webster]

WordNet (r) 3.0 (2006):

population
    n 1: the people who inhabit a territory or state; "the
         population seemed to be well fed and clothed"
    2: a group of organisms of the same species inhabiting a given
       area; "they hired hunters to keep down the deer population"
    3: (statistics) the entire aggregation of items from which
       samples can be drawn; "it is an estimate of the mean of the
       population" [syn: population, universe]
    4: 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: the act of populating (causing to live in a place); "he
       deplored the population of colonies with convicted criminals"