The Heliosphere is often described as a kind of bubble that contains our solar system. This magnetic sphere, which extends beyond Pluto, is caused by the Sun’s solar winds.
These winds spread out from the Sun at around 400 km/s until they hit what is known as interstellar space, which is also called local interstellar medium (LISM) or interstellar gas. Interstellar space is the space in galaxies that is unoccupied by either stars or planets.
When the solar winds hit local interstellar medium, a kind of bubble forms that prevents certain material from getting in. Thus, the heliosphere acts as a kind of shield that protects our solar system from cosmic rays, which are dangerous interstellar particles.
The Voyager Spacecraft have actively explored the outer reaches of the heliosphere, passing through the shock and entering the heliosheath, a transitional region which is in turn bounded by the outermost edge of the heliosphere, called the heliopause.
The heliopause is what separates the heliosphere and the interstellar gas outside the solar system. This is where the final frontier begins.