out-group 
noun
1 Sociology Those people who do not belong to a specific in-group.Racialized discourse is a set of social practices that favours the ingroup and denigrates the out-group, categorizing, evaluating and differentiating between groups....
- But the authoritarian adult is the kind of person whose view of the social world is extremely highly structured, and the structure is very much based on considerations of power strength, of in-groups and out-groups.
- The world is divided into in-groups and out-groups, with those who are different seen as enemies to be conquered or destroyed.
2 Biology A group of organisms not belonging to the group whose evolutionary relationships are being investigated. Such a group is used for comparison, to assess which characteristics of the group being studied are more widely distributed and may therefore be older in origin.The riverine group includes a small number of species and thus may serve as an out-group for comparison purposes....
- The plant mariner-like elements were used as a monophyletic out-group, a position suggested by previous analyses.
- Loligo bleekeri was used as the out-group in all phylogenetic analyses because most authors currently consider cephalopods as the sister group of gastropods.