"Spirit" is manifested by anything that combines subjectivity and objectivity. Objectivity is characterized by material nature-- objects have a beginning, an end, a composition, etc.
Subjectivity is characterized by consciousness, and even more so, self-consciousness. The subject, while still susceptible to external intentions, also produces its own intentions.
I won't weigh in on animals and their minds, but I label a human mind inside a human body as spirit. With my initial definition, it should be made clear that "spirit" can mean more than simply one individual. When two or more thinking people come together, for good or for ill, that too is a manifestation of spirit. A group of people is also a combination of objects and subjects, and so may be called "spirit."
Why call it Spirit?
In common usage, the phrase "human spirit" signifies a potential for greatness in humans as individuals or in groups. To me, this greatness can be thought of as both a depth and a height. There is a depth in the human experience, such that people are able to consider themselves, their actions, their relations, their place in the world, and the world itself-- indeed a person, by thinking and re-thinking, can contain the world and many possible worlds in their mind. There is a depth also between humans, found in the complexity of subterranean echoes that occur in almost every human interaction. We are more than meets the eye-- we are deep, and there is no need to invoke the idea of a "soul' in order to make this point. The vertical metaphor works in both directions, as "the human spirit" also indicates the new 'heights' that individuals and groups may attain. Feats of athleticism, moral courage, or simply getting up in the morning and heading to work/school-- we make 'more' of ourselves, transcending former limitations and definitions. We are more than meets the eye-- we contain in ourselves the future, and a promise of greatness. And there is no need to speak of God in order to make this point.
The word "spirit," to me, speaks to our potential for both depth and height. It also, quite conveniently, refers to the humanity of both the individual and the collective. In these ways, using the word "spirit" is helpful for me in order to think and speak about the human experience as a whole. Moreover, it captures for me the power (and thus the importance of considering seriously) of living as a subject/object. There is so much to say and respond to, being a subject-infused object and simultaneously an object-infused subject.
As Obama says before giving bad news, let me clear: to be spirit, whether individually or as a group, is to have the potential for both beauty and depravity. To borrow some language from religion, the human capacity for greatness can just as easily be demonic or angelic. The richness and complexity of the human experience produced the Renaissance and the Inquisition, the pyramids in Egypt and the slave labor that built those pyramids.
What is Spirituality?
Subjectivity sets spirits apart from the rest of the world of objects. As a subject, one has awareness, and that awareness has the ability to expand itself, to attempt to even include itself. To me, spirituality is about giving careful/caring attention to the fact that one can be self-aware. I take my inspiration for this definition from G.W.F Hegel's concept of internal critique--the process by which one can have ideals, attempt to fulfill them, and then re-assess whether one's actions are appropriate to the ideals, or whether the ideals themselves are appropriate at all. Our ability to "think twice" is a spiritual skill. Commitment to thinking twice is a spiritual practice.
There are many other spiritual skills/practices to be discussed, but for now I'll be happy that my blog definition of spirit has been written. If you found this confusing, I hope to say it all over again many other ways for the rest of my life. Also I hope to post the pamphlet definition of spirit, if someone will kindly tell me how to attach a pdf to a blog.