Source : Webster's Revised Unabridged Dictionary (1913)

Permutation \Per`mu*ta"tion\, n. [L. permutatio: cf. F.
   permutation. See {Permute}.]
   1. The act of permuting; exchange of the thing for another;
      mutual transference; interchange.

            The violent convulsions and permutations that have
            been made in property.                --Burke.

   2. (Math.)
      (a) The arrangement of any determinate number of things,
          as units, objects, letters, etc., in all possible
          orders, one after the other; -- called also
          {alternation}. Cf. {Combination}, n., 4.
      (b) Any one of such possible arrangements.

   3. (Law) Barter; exchange.

   {Permutation lock}, a lock in which the parts can be
      transposed or shifted, so as to require different
      arrangements of the tumblers on different occasions of
      unlocking.

Source : WordNet®

permutation
     n 1: an event in which one thing is substituted for another; "the
          replacement of lost blood by a transfusion of donor
          blood" [syn: {substitution}, {transposition}, {replacement},
           {switch}]
     2: the act of changing the arrangement of a given number of
        elements
     3: complete change in character or condition; "the
        permutations...taking place in the physical world"- Henry
        Miller
     4: act of changing the lineal order of objects in a group

Source : Free On-Line Dictionary of Computing

permutation
     
         1. An ordering of a certain number of elements
        of a given set.
     
        For instance, the permutations of (1,2,3) are (1,2,3) (2,3,1)
        (3,1,2) (3,2,1) (1,3,2) (2,1,3).
     
        Permutations form one of the canonical examples of a "{group}"
        - they can be composed and you can find an inverse permutation
        that reverses the action of any given permutation.
     
        The number of permutations of r things taken from a set of n
        is
     
        	n P r = n! / (n-r)!
     
        where "n P r" is usually written with n and r as subscripts
        and n! is the {factorial} of n.
     
        What the football pools call a "permutation" is not a
        permutation but a {combination} - the order does not matter.
     
        2. A {bijection} for which the {domain} and {range} are the
        same set and so
     
        f(f'(x)) = f'(f(x)) = x.
     
        (2001-05-10)