Noun
outer automorphism (plural outer automorphisms)
(algebra) An automorphism which is not an inner automorphism.
The other two subgroups are dihedral; these are permuted by an outer automorphism of the parent group, and are therefore not characteristic. Source: Internet
The extra outer automorphism in A 6 swaps the 3-cycles (like (123)) with elements of shape 3 2 (like (123)(456)). Source: Internet