A soul is a self-arising desire to exist. It is an extension of our Source. You are an extension of your Source. Simply put, your soul is your "desire to exist." A fancy way of putting it is, our Soul is an "individuation of eternal spirit." It is the reason why you are here in this body, and why you will reincarnate into another one, ad infinitum. Existence itself began as an intention to "be." We are individual extensions of that primordial intention to Be. 

Hope all that makes sense. Take it easy and stay tuned for more.