What is a soul?

This was the hot topic of our final public theology class. The most heated part of the discussion (respectful, but strongly worded!) was on the topic of abortion, choice, and fatherhood. I've rehashed that debate often enough (the organization I work for is, as a matter of conscience and integrity with our mission of empowerment, pro-choice). I would like to share some of the other thoughts that came up -

What is a soul? My (current) answer , informed by prior thought and important contributions from classmates- the soul is that in us which reaches outward towards God and community. When we choose to isolate ourselves, or are forced into isolation by circumstance, I believe that vital God-spark in us diminishes. I believe, from seeing it in others, and experiencing it myself, that it can be nurtured back to health, but it is a long road. Kudos to a classmate for his comments on relationality that pushed me to sharpen my thoughts on the issue.
Just the same, when we over-extend, and neglect the nurture of our own soul (it takes a certain level of strength to reach out to others), we must tend our own gardens (apologies to Voltaire...), for a while, so that capacity to relate can be recharged. A classmate said, "I believe our souls learn, grow and expand when we attend to them." Hear, hear!
Yes, it's your friendly neighborhood introvert talking, but I think the sentiment would still hold for extroverts, to a different degree. [Extroverts - speak up! Do I have you all wrong?]
It is the balance of relationality and solitude for reflection that nurtures the soul. The gardener in me recognizes we need both light and dark (makes me want to re-read John of the Cross) to grow. Essential processes occur in both sides of the cycle. I'm too lazy to get my old plant physiology book out, but my recollection is that the plant breathes CO2 and exhales oxygen at different times of the day.

What do you think the soul is? Are there other metaphors you would suggest besides a plant? I'm always looking for items for my toolkit!