From BiblePortal Wikipedia

Webster's Dictionary [1]

(n.) A fountain on Mount Helicon in Boeotia, fabled to have burst forth when the ground was struck by the hoof of Pegasus. Also, its waters, which were supposed to impart poetic inspiration.

The Nuttall Encyclopedia [2]

The fountain of the horse), a fountain on Mount Helicon, in Boeotia, sacred to the Muses, and said to have been caused by Pegasus ( q. v .) striking the spot with his hoof.