The Probert Encyclopaedia of Music

ENHARMONIC

In ancient music, enharmonic was a kind of musical scale recognised by the ancient Greeks, which consisted of quarter tones and major thirds, and was regarded as the most accurate. In modern music, the term enharmonic pertains to a change of notes to the eye, while, as the same keys are used, the instrument can mark no difference to the ear, as for example the substitution of A flat for G sharp.
Research Enharmonic