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Disk galaxy is a term for disk-shaped galaxies (e.g., as opposed to elliptical galaxies), including spiral galaxies, and including galaxies that are generally disk-shaped, even if they have a bulge, such as lenticular galaxies. The term disk refers to the galaxy's disk-like feature, often not intended to include the protrusions of any bulge. Some observation and analysis suggests the disks of galaxies often can be distinguished to be overlaid disks of distinctive stars, each with its distinctive gas, dust, and kinematic characteristics. In the case of the Milky Way, a thick disk (of thick disk stars) has within it, a thin disk (of thin disk stars), the latter apparently younger, the result of more recent star formation.