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Stellar overdensity (often just overdensity) is a term used for a portion of the galactic halo with a noticeably greater density of stars than elsewhere, but is something less than a satellite galaxy, and lacks the form of a stellar stream (long and narrow) or a globular cluster (spherical and extremely dense with stars). The past few years have seen considerable discoveries of all of these, due to improvements in technology and deployment of new equipment, such as Gaia.