Final answer:
The central portion of a spiral galaxy that bulges above and below the plane of the galactic disk is known as the bulge.
Step-by-step explanation:
The central portion of a spiral galaxy that is roughly spherical (or football shaped) and bulges above and below the plane of the galactic disk is called the bulge. This structure is composed mostly of old stars and is part of the main components of a spiral galaxy, which also includes a halo, a disk, and spiral arms. The bulge of the Milky Way, our own galaxy, also contains a supermassive black hole at its very center. Spiral galaxies like the Milky Way and the Andromeda galaxy exhibit such a feature, with the bulge visible as a distinct peanut-shaped structure around the galactic center.