What is the space between the extent of one solar system and another called?

The space between the extent of one solar system and another is referred to as interstellar space. This term accurately describes the vast regions that exist between individual stars and their respective solar systems within a galaxy. Interstellar space is characterized by low densities of particles and radiation as it serves as a transition zone between solar systems.

In contrast, intrastellar space, which is not a commonly used term, would imply the area within a star rather than between them; hence it doesn't relate to the context of solar systems. The term solar gap is not a standard astronomical term and does not have recognized meaning in the context of cosmic distances. Finally, the galactic void refers to much larger empty spaces between clusters of galaxies, which is distinct from the concept of the space specifically between solar systems within a galaxy. Thus, interstellar space is the precise term that correctly defines the area in question.