Another word for the Sun, derived from Latin. This noun is not common in general usage, although the related adjective "solar" is. It seems to be more commonly used in science fiction writing, perhaps to avoid the geocentric associations of the word "Sun".
The term sol has also been used by NASA engineers, in unmanned Mars mission operations, to refer to a solar day on Mars. (An Earth day is 24 hours long, a Mars day or "sol" is 24 hours, 37 minutes long.)