I interpret it as the search for understanding the true nature of existence, consciousness, self realization as a spirit in a body - opposed to just being a body - and existences outside our own.
I can imagine spirituality being interpreted in different ways, which could be what the very essence of spirituality is, looking to yourself for answers about the the unknown.
A few sources of reference:
What is Spirituality?
What is Spirituality?
Wikipedia Definition
So, how do you interpret spirituality?