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The term subgroup (for galaxy subgroup) is used for a subgroup of a galaxy group or galaxy cluster, presumably consisting of galaxies distinguished from others by proximity and possibly other characteristics. A common use of subgroup is for some significant galaxy plus its satellite galaxies: in this case, proximity is strongly suggestive, but the host/satellite relationship can be further checked using mass and velocity determinations, and in some cases, metallicity determinations. Within the Local Group, the term is used for the Milky Way subgroup, the Andromeda subgroup (aka M31 subgroup) and the Triangulum subgroup (aka M33 subgroup).