Soul is that which has no predicate.  It also can be laughing out loud for no apparent reason.

A soul to me is something that lets the body live. Like a plant it doen't feel pain or love it just lives. Well that what I think anyways.

I personally feel that "soul" is the "heart of our essence"... love in its purest form, unconditional and never ending.

Definitions are limiting.  The things that matter cannot be limited to definitions.  Love.  Truth.  And soul.  I know that this does not answer your question.  I just can't think of a definition that would suffice so the best response is ...

In my own limited understanding, my soul is my mind; not my intellectual mind, but the part of me which travels through the vast ocean of time, light and even space, to ultimately re-unite with the greater universal mind/soul which some may call god, some other god/goddes...