As the solar wind streams out of the solar system it eventually runs into the interstellar medium. The heliosphere, the region where the solar wind and the interplanetary magnetic field pulled out of the Sun by the solar wind are unaffected by the interstellar medium, consists of a bubble-shaped region surrounding the Sun. In the direction the Sun moves through the interstellar medium a bow shock is formed similar to that in between the magnetic field of the Earth and the interplanetary magnetic field; and in between the bow shock and the heliosphere is the heliosheath, a region where the effects of the interstellar medium are mingled with that of the heliosphere. The image below shows the geometry involved, and should be compared to the image of
The Magnetic Field of the Earth.
(Walt Feimer, NASA)