In context|systematics| the difference   between ingroup and outgroup is that ingroup is (systematics) in cladistics,   the monophyletic group that includes all taxa of interest to the current   study while outgroup is (systematics) in cladistics, all the taxa included in   a study that do not belong to the ingroup that is of immediate interest.

从系统学的角度来看，内外群的区别在于外群是支序分类学（系统学），中的一个单系群，它包括了当前研究中所有感兴趣的类群，外群是我们直接感兴趣的内群以外的所有类群。