noun Astronomy.
the boundary of the heliosphere.

1970–75; helio- + pause

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World English Dictionary
heliopause (ˈhiːlɪəʊˌpɔːz)
the boundary between the region of space dominated by the solar wind and the interstellar medium

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American Heritage
Science Dictionary
heliopause   (hē'lē-ə-pôz')  Pronunciation Key 
The region surrounding the solar system at which pressure from the outgoing solar wind equals the pressure from the interstellar medium (made up mostly of hydrogen and helium), and the solar wind can penetrate no further. It is considered to be the outer boundary of our solar system. See more at solar wind.
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