The heliosheath is the zone between the termination shock and the heliopause at the outer border of the solar system. It lies along the edge of the heliosphere, a "bubble" caused by solar winds.

The heliosheath's distance from the Sun is approximately 80 to 100 astronomical units (AU). The current mission of the Voyager 1 and Voyager 2 space probes includes studying the heliosheath.

In May 2005, NASA announced that Voyager 1 had crossed the termination shock and entered the heliosheath in December 2004, at a distance of 94 AU. An earlier report that this had occurred in August 2002 (at 85 AU) is now generally believed to have been premature.