Final answer:
A flat, disc-shaped galaxy with curved arms fanning out is described as a Spiral galaxy, which has a central bulge and spiral arms where new stars form.
Step-by-step explanation:
The description of a flat, disc-shaped galaxy with curved arms fanning out refers to a Spiral galaxy. Spiral galaxies are characterized by a central bulge surrounded by a disk and curved spiral arms. These arms are sites of ongoing star formation and are often populated with bright emission nebulae and hot, young stars. While they may come in variations, with the central bulge and the arms varying in prominence, the defining feature is the presence of these arms extending from the center. Spiral galaxies, such as our own Milky Way and the Andromeda galaxy, are distinct from elliptical galaxies which have an ellipsoidal shape with no spiral arms and consist mostly of older stars. They are also different from irregular galaxies that lack a distinct shape, and from lenticular galaxies that may have a disk but do not show the prominent spiral arms.