ingroup

kuppikunta puhekieltä In cladistics, the monophyletic group that includes all taxa of interest to the current study.
2009 January 15, Martin D. Brazeau, “The braincase and jaws of a Devonian 'acanthodian' and modern gnathostome origins”, 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.

You will learn a lot about formal and informal Japanese language throughout this book. In Japanese society a distinction is made between the 'in-group' (myself, my family, my work colleagues, my friends) and the 'out-group' (my seniors, people from other families and workplaces). Politeness is an important traditional aspect of Japanese life and this is reflected strongly in the language used when speaking to those in the out-group. More informal language is generally used within the in-group.