Atheists: what is "spirituality"?

[Belacqua]

The definition is fuzzy because the concept is fuzzy, and the concept is fuzzy because the things it's trying to describe are not valued or encouraged in our society.

A subjective sense of belonging in the universe, and a feeling of solidarity with other living things, cannot be quantified, packaged for sale, or weaponized. But it can be easily mocked, by portraying spiritual people as unserious and a bit loony. 

But feelings really exist, and how people feel is important. So the fact that the word is weak is a sign that some important things are also weak.

Per Wikipedia:

Spirituality is the quality of being attached to or concerned with religious questions and values broadly conceived, although the term is loosely defined, and may mean different things in different contexts. Traditionally, spirituality referred to a religious process of re-formation which "aims to recover the original shape of man", oriented at "the image of God" as exemplified by the founders and sacred texts of the religions of the world. The term was used within early Christianity to refer to a life oriented toward the Holy Spirit and broadened during the Late Middle Ages to include mental aspects of life.

In modern times, the term both spread to other religious traditions and broadened to refer to a wider range of experiences, including a range of esoteric and religious traditions. Modern usages tend to refer to a subjective experience of a sacred dimension, and the "deepest values and meanings by which people live", often in a context separate from organized religious institutions. This may involve belief in a supernatural realm beyond the ordinarily observable world, personal growth, a quest for an ultimate or sacred meaning, religious experience, or an encounter with one's own "inner dimension" or spirit.

Some spiritual people are "unserious and a bit loony," whether they are mocked for it or not.  That is likely because the idea of spirituality is so poorly defined that they try all sorts of things.

Yes, I think this is exactly right. As the Wikipedia article describes, spirituality used to be more closely associated with Christianity. That meant that there were authorities defining how it should be. 

Now that Christianity has lost so much of its cultural importance, this leaves the "deepest values and meanings" field open for individual interpretation. So of course freedom of choice is good, but of course a lot of people are going to end up with something silly. 

And of course we are a part of our ecological systems, whether we understand that or not.  We don't have to seek it, just to acknowledge it and to do something about it.

But I would say that a scientific knowledge of our place in the ecosystem is not the same as a spiritual sense of belonging. Christians had the feeling that the universe cared about what they did, even if they were socially insignificant. A scientific worldview confirms our insignificance. Spirituality, as I understand it, has something to do with an affirmation of one's belonging. Even if, after your ayahuasca trip, you think of yourself as a speck in the Great Mind of Nature (or whatever) at least you feel there's a meaning behind it all. 

"How people feel is important."  I will have to work on that one for obvious reasons.  As I admitted, I seem to lack ordinary emotional intelligence.

I don't know about your emotional intelligence... I certainly won't judge that. 

Don't you think that a society in which people feel fulfilled is to be desired, as opposed to a society in which people are mostly miserable? That's putting it in extreme terms (exaggerated for clarity) but I think that if a given culture tends to give people the tools they need to flourish, then that's a good thing. And flourishing is surely more than material wealth. (Someplace I read that the most common complaint Americans have when they go to a psychologist is that they have everything they want but they still aren't happy. I don't know if that's true or not, but it makes sense.) 

Spirituality is, currently, a rather unorganized concept that people use when they're trying to fulfill certain (perceived) needs.