Source : Webster's Revised Unabridged Dictionary (1913)

Prevalence \Prev"a*lence\, n. [L. praevalentia: cf. F.
   pr['e]valence. See {Prevail}.]
   The quality or condition of being prevalent; superior
   strength, force, or influence; general existence, reception,
   or practice; wide extension; as, the prevalence of virtue, of
   a fashion, or of a disease; the prevalence of a rumor.

         The duke better knew what kind of argument were of
         prevalence with him.                     --Clarendon.

Source : WordNet®

prevalence
     n 1: the quality of prevailing generally; being widespread; "he
          was surprised by the prevalence of optimism about the
          future"
     2: (epidemiology) the ratio (for a given time period) of the
        number of occurrences of a disease or event to the number
        of units at risk in the population
     3: a superiority in numbers or amount; "there is a
        preponderance of Blacks in our prisons" [syn: {preponderance}]