The Christian festival (January 6th) commemorating the presentation of Christ to the Magi (the three wise men who followed the star to Bethlehem). Hence, a moment of spiritual revelation. An aesthetic of the epiphany is developed by James Joyce's hero Stephen Dedalus in A Portrait of an Artist as a Young Man where he argues from Aquinas that an epiphany is a revelation of the particular quidditas or 'whatness' of an experience or thing.
Editors. "Epiphany". The Literary Encyclopedia. First published 01 November 2001
[http://www.litencyc.com/php/stopics.php?rec=true&UID=347, accessed 20 June 2013.]