What term describes the space within galaxies?

The term that accurately describes the space within galaxies is intragalactic space. This refers to the regions and volumes contained within the boundaries of a galaxy, encompassing everything from stars and stellar systems to gas, dust, and dark matter that exists in those regions.

While interstellar space refers to the space between stars within a galaxy, intragalactic space encompasses the entire volume of the galaxy, including both the interstellar medium and the galactic structure itself. Cosmic voids, on the other hand, refer to large areas of space in the universe that are relatively empty and do not contain many galaxies, which is a different concept entirely. Lastly, a galactic halo describes a specific component of a galaxy's structure, typically consisting of dark matter and older stars that are found surrounding the main body of the galaxy, rather than the broader concept of the space within the galaxy itself.