Galaxies are categorized according to their apparent shape. These shapes are typically divided into elliptical, spiral, or irregular. The shape of a galaxy gives a clue to the age and types of stars within the galaxy. Spiral galaxies have a central bulge of stars surrounded by a disk that contains arms, which form a spiral structure. Stars in the bulge of a spiral galaxy tend to be older and redder than the rest. There's also a much fainter, roughly spherical, stellar halo encompassing the disk. An example of a spiral galaxy is one of our nearest neighbors, the Andromeda galaxy. Barred spiral galaxies are spiral galaxies with a bar of stars across the middle of the galaxy. The Milky Way is thought to be a barred spiral galaxy, as are about 2/3 of all observed spiral galaxies.

Source: Britannica