A Heliopath is allegedly, a spirit of fire which gallops and burns anything in its path. This is one of the many creatures Luna Lovegood asserts exist, but which is not documented anywhere else. She once claimed that the former Minister for Magic Cornelius Fudge had an army of these creatures at his command, though given his ineptitude for leadership, as well as Luna's beliefs being dubious, this is unlikely. She also claimed there were plenty of eye-witnesses to their existence.
The name "Heliopath" appears to derive from the Greek hḗlios meaning "sun" (and therefore also the name of a Greek solar deity) combined with the suffix "-path" from Greek páthos meaning "suffering, sensation". Therefore, a Heliopath means "sun sensation/sensation of the sun" or (more correctly) "something which feels like the Sun" - a fitting description (assuming that these creatures exist at all). Alternately, given their attribute of burning everything in their path, it could be correct to say they are or they bring "suffering like that of the Sun" - an intense heat, certainly.
- Harry Potter and the Order of the Phoenix (Mentioned only)