Outer Automorphism Group

A particular type of Automorphism Group which exists only for Groups. For a Group $G$, the outer automorphism group is the Quotient Group $\mathop{\rm Aut}\nolimits (G)/\mathop{\rm Inn}\nolimits (G)$, which is the Automorphism Group of $G$ modulo its Inner Automorphism Group.

See also Automorphism Group, Inner Automorphism Group, Quotient Group