Source : Webster's Revised Unabridged Dictionary (1913)

Concentration \Con`cen*tra"tion\, n. [Cf. F. concentration.]
   1. The act or process of concentrating; the process of
      becoming concentrated, or the state of being concentrated;
      concentration.

            Concentration of the lunar beams.     --Boyle.

            Intense concetration of thought.      --Sir J.
                                                  Herschel.

   2. The act or process of reducing the volume of a liquid, as
      by evaporation.

            The acid acquires a higher degree of concentration.
                                                  --Knight.

   3. (Metal.) The act or process of removing the dress of ore
      and of reducing the valuable part to smaller compass, as
      by currents of air or water.

Source : WordNet®

concentration
     n 1: the strength of a solution; number of molecules of a
          substance in a given volume (expressed as moles/cubic
          meter)
     2: the spatial property of being crowded together [syn: {density},
         {denseness}, {compactness}] [ant: {distribution}]
     3: strengthening the concentration (as of a solute in a
        mixture) by removing extraneous material [ant: {dilution}]
     4: increase in density
     5: complete attention; intense mental effort [syn: {engrossment},
         {absorption}, {immersion}]
     6: bringing together military forces
     7: great and constant diligence and attention [syn: {assiduity},
         {assiduousness}]