Heliophysics is a word coined by Dr. George Siscoe of Boston University and subsequently used by the NASA Science Mission Directorate to encompass the study of the system composed of the Sun's heliosphere and the objects that interact with it -- most notably, but not limited to, planetary atmospheres and magnetospheres, the solar corona, and the interstellar medium. Heliophysics combines several other disciplines, including several branches of space physics, plasma physics, and solar physics. Heliophysics is closely tied to the study of space weather and the phenomena that affect it. To quote George Siscoe from a recent conference presentation:“Heliophysics is an environmental science, a unique hybrid between meteorology and astrophysics. It comprises a body of data and a set of paradigms (general laws—perhaps mostly still undiscovered) specific to magnetized plasmas and neutrals in the heliosphere interacting with themselves and with gravitating bodies and their atmospheres.”

Heliophysics is one of four divisions within NASA's Science Mission Directorate (Earth Science, Planetary Science, Heliophysics, and Astrophysics. The word was used to simplify the name of the "Sun Solar System Connections" Division (and before that, the "Sun-Earth Connections" Division). There is some controversy behind the naming of this division, since the base-word "Helio" means sun. The word "Heliophysics" literally means "Physics of the Sun", which, therefore, does not adequately describe the majority of the science that is conducted within the Heliophysics division.

Use of the word heliophysics has also extended to the recent International Heliophysical Year in 2007-2008.