So here's my best shot: Spirituality is an awareness of the gap between what you can experience and what you can describe.This is the best definition I've ever heard. If it does not make immediate sense to you then I suggest you read his post which goes into detail on his thought process and the context in which that process was engaged.
02 September 2010
Muder on Spirituality (responding to humanist concerns)
Here's what Doug Muder considers to be spirituality: