The best definition I've been able to come up with is that spirituality is basically the relationships you have with yourself, with others, your work, the food you eat, your religious practices, etc. To me at least spirituality isn't especially vague, it's something that you could probe and measure (to some extent), not unlike the social graph on Facebook.

"You meant something like 'if I'm driving my car, and an animal runs in front of my, my body reacts before I am consciously aware of it'."

More like my legs started walking on their own without any conscious input from me.

"This is true, but I'm not sure what this has to do with spirituality."

The kinds of answers you give to the relationship questions I posed above are largely dependent on your worldview and how you think the universe works. After meditating you start to experience the world differently at the experiential level, and because of this how you view the universe naturally changes. And because of this your view on all those spirituality type questions I started to enumerate in my definition also changes.