It’s a word that I tend to not use.  It seems to me like a word that can mean a great many different things depending on who’s saying it and the context.  It seems like a word that can be spoken by one person, who has a meaning in mind, and received by another who interprets it as meaning something entirely different.  It can mean living in a cave for 10 years or appreciating the beauty of a rainbow.  Or almost anything in between.

Wikipedia is fairly clear.

Spirituality refers to an ultimate or an alleged immaterial reality; an inner path enabling a person to discover the essence of his/her being; or the “deepest values and meanings by which people live.” Spiritual practices, including meditationprayer and contemplation, are intended to develop an individual’s inner life; spiritual experience includes that of connectedness with a larger reality, yielding a more comprehensive self; with other individuals or the human community; with nature or the cosmos; or with the divine realm.[3] Spirituality is often experienced as a source of inspiration or orientation in life.[4] It can encompass belief in immaterial realities or experiences of the immanent or transcendent nature of the world.

Of course it does require you to know what an “ultimate or immaterial reality” might be.  Or what is meant by an “inner path”, or a “divine realm”, or quite a bit else.  I don’t think it would necessarily be something you could explain to an alien visitor. It’s one of those words who’s definition is self referential.

Here are a couple comments I’ve found on the web.

“Spiritual” is a poorly defined word. It can mean whatever you want it to mean, which makes it rather useless.

Some people use it to define their own sort-of religion they’ve pieced together from other beliefs. Others use it to define an imagined connection between themselves and other living things. Quite a few people use it to explain a sense of awe with the world.

I avoid the word because of its fuzzy meanings and religious connotations. I’m not at all spiritual. Yet, I am in awe, every day, of so many things I observe and experience. The interaction between friends, and strangers, the beauty of flower or a weed, the taste of fresh sweet corn, the size of the universe, the touch of a lover, the experience of a fine cigar, the affection of a loyal dog, the thrill of making a perfect meal, the joy of a finely crafted sentence, the emotions evoked by music of all sorts, the inspiration of a painting, the brutal honesty of children, the humor all around us – it’s a very, very long list.

I am often in awe and would never diminish the emotion by calling it something as lame as “spiritual.”
Dave Hill 

‘Spiritual’ is a weaselly word, much beloved of people who are trying to sneak in the entirely unsubstantiated idea that there is more to life and the universe than will ever be able to be accounted for in material, naturalistic terms.

It seems to be used in two main ways.

When someone talks of being ‘spiritual but not religious’ it normally means they don’t follow a religion as such but cling to the idea that there’s a higher power of some kind, or something mystical about the universe. I would suggest that being spiritual, in this sense, is as irrational as being religious, since neither position has any evidence to support it.

There is another use of the word which isn’t of itself irrational, but which is unhelpful and unnecessary, because it is too often used – either by the speaker or the listener, or both – to sneak mysticism in by the back door. This is when people talk of ‘spiritual well-being’. I have not encountered a non-religious use of that term that would not have been rendered better as ’emotional and psychological well-being’, a much more neutral and rational idea and one which clearly does not require religion or any other form of mysticism.
Paula Kirby

I don’t know who those people are – I found them on an atheist discussion board.  I do find their comments interesting.  If you are irritated by their comments, I’d love to hear why.  I often feel alone in my reaction to that word.  Most everyone seems to use it and fell comfortable with it, but I don’t.