Wikipedia says the definition of interplanetary space is
the region dominated by the interplanetary medium, which extends out to the heliopause where the influence of the galactic environment starts to dominate over the magnetic field and particle flux from the Sun
While it defines the solar system as the region in which the sun is the primary gravitational influence
The Sun's gravitational field is estimated to dominate the gravitational forces of surrounding stars out to about two light years (125,000 AU).
So, if the region outside the heliopause but inside the solar system isn't interplanetary space, then what is it?