The part of outer space within the solar system WordNet 3.0 & Open English WordNet

Space extending between the sun and the planets of the solar system. Interplanetary space is not empty, but contains dust, particles with an electric charge, and the magnetic field of the sun (also called the IMF, or Interplanetary Magnetic Field). OmegaWiki

That part of outer space between the planets of a solar system and its star. Wiktionary