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The term dwarf spheroidal galaxy is used for some dwarf galaxies in the Local Group that have a somewhat spherical shape, a low luminosity, and little gas, dust, or star formation. Examples:
Dwarf spheroidal galaxies (or at least some of them) have shown velocity dispersions indicating a larger ratio of dark matter (DM) to gas/stars than typical, those with such a larger ratio called DM-dominated dwarf spheroidals. Explaining this has motivated research: it is presumed that galaxies form over regions of high DM density, motivating models make less stars and gas form, or cause the galaxy to lose some. Other explanations make particular suggestions about the nature of dark matter itself.