Words at Play : Top 10 User-Submitted Words, Vol. 5
Definition:
(noun) a precise point in time in which one has sudden understanding of or insight into something
Example:
... [S]he had that "aha moment" in the summer of 2009 when an old photo of her slimmer self made her decide it was time she took charge of her weight. Susan Pierce, Times Free Press, September 9, 2010