Sam Harris has suggested the secular humanist movement reclaim the word "spirit." Though you may think otherwise, this word can have a secular definition. A definition unencumbered by the assumption of an afterlife or any notion of the supernatural at all. Harris would like to untangle the word spirit from "its association with medieval superstition."
I comprehend this word in a literal sense. This is known as the Epicurean definition. Spirit translates from the Latin for breathe. This conceptual syntax can be seen in words like "inspire" "aspire" and "perspire." Indeed, an alternate definition of "inspiration" is to "breath in."
With this in mind I see the spirit not as metaphorical but as real.
All people "breathe" their spirit into the world by their interactions with people around them. Someone can breathe their spirit into the world by writing a thousand page tome on moral philosophy, or simply smiling at a child.
In any case these spiritual expressions I see as the path to immortality (not by living in some imaginary afterlife) but by actually influencing the world of the living after we have died. Living on through the "extra soma" though this phrase has more to do with living on through writing more so than actions.
Many different forces have formed my own view of the word "spirit" most notably my own Swedish grandmother. We called her "Zsage" though her name was Doris. She still has a daily influence on my life. Not that I speak with her on some astral plain but I'm reminded of her wisdom, in the garden, the kitchen, and in the studio by all kinds of memory ques.
I hope this explains what I think "spirit" means. I have written these thoughts before in different ways. Read additional thoughts here.
Also, the following videos have influenced my view on this topic. The fist is a segment from an interview with the writer Margaret Atwood, and second a speech by historian Doris Kearns Goodwin. Goodwin's speech is particularly poignant in explaining Abraham Lincoln's Epicurean perspective on the afterlife. Famed professor of animal sciences Temple Grandin speaks of the "extra soma" in the last chapter of her famous "thinking in pictures" book as well.