Source : Webster's Revised Unabridged Dictionary (1913)

Circulation \Cir`cu*la"tion\, n. [L. circulatio: cf. F.
   circulation.]
   1. The act of moving in a circle, or in a course which brings
      the moving body to the place where its motion began.

            This continual circulation of human things. --Swift.

   2. The act of passing from place to place or person to
      person; free diffusion; transmission.

            The true doctrines of astronomy appear to have had
            some popular circulation.             --Whewell.

   3. Currency; circulating coin; notes, bills, etc., current
      for coin.

   4. The extent to which anything circulates or is circulated;
      the measure of diffusion; as, the circulation of a
      newspaper.

   5. (Physiol.) The movement of the blood in the blood-vascular
      system, by which it is brought into close relations with
      almost every living elementary constituent. Also, the
      movement of the sap in the vessels and tissues of plants.

Source : WordNet®

circulation
     n 1: the dissemination of copies of periodicals (as newspapers or
          magazines)
     2: movement through a circuit; especially the movement of blood
        through the heart and blood vessels
     3: (library science) the count of books that are loaned by a
        library over a specified period
     4: number of copies of a newspaper or magazine that are sold;
        "by increasing its circulation the newspaper hoped to
        increase its advertising"
     5: free movement or passage through a series of vessels (as of
        water through pipes or sap through a plant)
     6: the spread or transmission of something (as news or money)
        to a wider group or area