n.  1.  The act of permuting; exchange of the thing for another; mutual transference; interchange.  
2.  (Math.) The arrangement of any determinate number of things, as units, objects, letters, etc., in all possible orders, one after the other;  called also  
3.  (Law) Barter; exchange.

Noun  1.  permutation  an event in which one thing is substituted for another; "the replacement of lost blood by a transfusion of donor blood" 
2.  permutation  the act of changing the arrangement of a given number of elements  
3.  permutation  complete change in character or condition; "the permutations...taking place in the physical world" Henry Miller  
4.  permutation  act of changing the lineal order of objects in a group 
PERMUTATION, civil law. Exchange; barter.
2. This contract is formed by the consent of the parties, but delivery
is indispensable; for, without it, it mere agreement. Dig. 31, 77, 4; Code,
4, 64, 3.
3. Permutation differs from sale in this, that in the former a delivery
of the articles sold must be made, while in the latter it is unnecessary. It
agrees with the contract of sale, however, in the following particulars: 1.
That he to whom the delivery is made acquires the right or faculty of
prescribing. Dig. 41, 3, 4, 17. 2. That the contracting parties are bound to
guaranty to each other the title of the things delivered. Code, 4, 64, 1. 3.
That they are bound to take back the things delivered, when they have latent
defects which they have concealed. Dig. 21, 1, 63. See Aso & Man. Inst. B.
2, t. 16, c. 1; Nutation; Transfer.
(mathematics)  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! / (nr)! 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. 