What is Permutation?

Legal Definition
In mathematics, the notion of permutation relates to the act of arranging all the members of a set into some sequence or order, or if the set is already ordered, rearranging (reordering) its elements, a process called permuting. These differ from combinations, which are selections of some members of a set where order is disregarded. For example, written as tuples, there are six permutations of the set {1,2,3}, namely: (1,2,3), (1,3,2), (2,1,3), (2,3,1), (3,1,2), and (3,2,1). These are all the possible orderings of this three element set. As another example, an anagram of a word, all of whose letters are different, is a permutation of its letters. In this example, the letters are already ordered in the original word and the anagram is a reordering of the letters. The study of permutations of finite sets is a topic in the field of combinatorics.

Permutations occur, in more or less prominent ways, in almost every area of mathematics. They often arise when different orderings on certain finite sets are considered, possibly only because one wants to ignore such orderings and needs to know how many configurations are thus identified. For similar reasons permutations arise in the study of sorting algorithms in computer science.

The number of permutations of n distinct objects is n factorial, usually written as n!, which means the product of all positive integers less than or equal to n.

In algebra and particularly in group theory, a permutation of a set S is defined as a bijection from S to itself. That is, it is a function from S to S for which every element occurs exactly once as an image value. This is related to the rearrangement of the elements of S in which each element s is replaced by the corresponding f(s). The collection of such permutations form a group called the symmetric group of S. The key to this group's structure is the fact that the composition of two permutations (performing two given rearrangements in succession) results in another rearrangement. Permutations may act on structured objects by rearranging their components, or by certain replacements (substitutions) of symbols.

In elementary combinatorics, the k-permutations, or partial permutations, are the ordered arrangements of k distinct elements selected from a set. When k is equal to the size of the set, these are the permutations of the set.
-- Wikipedia
Legal Definition
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.
-- Bouviers Law Dictionary
Legal Definition
The exchange of one movable subject for another; barter.
-- Black's Law Dictionary
Legal Definition
Exchange; barter.
-- Ballentine's Law Dictionary