(systematics) In cladistics, all the taxa included in a study that do not belong to the ingroup that is of immediate interest.
2009 January 15, Martin D. Brazeau, “The braincase and jaws of a Devonian 'acanthodian' and modern gnathostome originsâ€, Nature Volume 457 No. 7227, doi:10.1038/nature07436: A cladistic analysis of 45 ingroup and two outgroup taxa was performed on the basis of 134 characters.
(sociology) The group of people who do not belong to one's own social group.
