What Is Spirituality?

There seems to be a frustrating but unavoidable opinion in our culture that "spirituality" is associated with being good, and "materialism" (in the colloquial sense of "he who dies with the most toys wins") is associated with being wicked. I've encountered it several times recently in discussions here, usually in the context of saying that atheists just don't "get" religion, that we're "missing the point". Presumably, religion is supposed to deal with the "spiritual dimension" of human experience, and never mind all the times it ignores the supposed boundaries of its magisterium. Because atheists don't believe in god or the supernatural, they can't be spiritual, and thus can't really be good. The psychologist Nicholas Humphrey described it thus, when noting that all stories of psychic phenomena have self-righteous, "holy" elements:

...it originates with what is, arguably, one of the most remarkable confidence tricks our culture has played on us. This has been to persuade people that there is a deep connection between believing in the possibility of psychic forces and being a gracious, honest, upright, trustworthy member of society...

The majority of our culture seems to be convinced, across religious views, that humans have a "deep need" for "spirituality." But what does spirituality mean? I guess it's supposed to be obvious, because very rarely does anyone even try to explain it. It's not at all obvious. The typical answer, which I've also received here many times in similar contexts, is "If you have to ask, you'll never know; you have to live it." Which is singularly worthless as an explanation; it is indeed a refusal to explain. Dan Dennett parodies, rather accurately as all good parodies do, the typical explanation. To see how hard it is to explain what spirituality is, he challenges his readers to try to improve on this:

"Spirituality is, you know, like, it's like paying attention to your soul or having deep thoughts that really move you, and not just thinking about who's got nicer clothes and whether to buy a new car and what's for dinner and stuff like that. Spirituality is really caring and not being just, you know, materialistic."

And, of course, it's easy to make the jump from "only thinking about stuff" materialistic to "all phenomena are explicable without an appeal to immaterial things" materialistic. At which point, it's effortless to slide into thinking that atheists don't "really care", are shallow and selfish and overconfident know-it-alls, when they're "missing out" on this vague, poorly defined, and yet oh so important dimension of human experience, the spirit.

Dennett goes on to try to give better words to what spirituality is:

What those people have realized is one of the best secrets to life: let your self go. If you can approach the world's complexities, both its glories and its horrors, with an attitude of humble curiosity, acknowledging that however deeply you have seen, you have only just scratched the surface, you will find worlds within worlds, beauties you could not heretofore imagine, and all your own mundane preoccupations will shrink to proper size, not all that important in the greater scheme of things. Keeping that awestruck vision of the world ready to hand while dealing with the demands of daily living is no easy exercise, but it is definitely worth the effort, for if you can stay centered, and engaged, you will find the hard choices easier, the right words will come to you when you need them, and you will indeed be a better person.

And then he gives the all-important point (emphasis mine):

That, I propose is the secret to spirituality, and it has nothing at all to do with believing in an immortal soul, or in anything supernatural.

There is absolutely nothing stopping an atheist from understanding that feeling, having that mindset of awe and wonder and proper scale and connectedness and humility. Indeed, most of the atheists I've talked to understand this quite deeply; how many upvotes are given to We Are Star Dust or The Story of Everything or This Remarkable Thing or A Universe Not Made For Us? If this is what spirituality means, then almost every atheist I know is deeply spiritual. If it's not what spirituality means, then what does it mean? I'd really love for someone to explain to me, clearly and understandably, what I'm "missing out on" by not being religious.