Meaning of even permutation

e'ven permuta'tion

Pronunciation: [key]
— Math. Math.
  1. a permutation of a set of n elements, x, x, … x, that leaves unchanged the product of all differences of the form (x — x), where i is less than j. Cf. odd permutation.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.