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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, e.g., lenticular galaxy. The term disk refers to the galaxy's disk-like feature, often not intended to include the protrusions of the bulge.
Some analysis of observation suggests a majority of disk galaxies (including the Milky Way) comprise two overlaid disks of stars: a thick disk (i.e., thick disk stars), and within it, a thin disk (thin disk stars) that also includes gas, and dust. The thin disk stars are apparently younger, the result of more recent star formation.