Soul, Spirit, Atman, Self etc. are words which are used to define subtle nature of ourselves which is invisible & mysterious. Soul is something which is within this body & something which can exist without this body. When soul lives in this physical body then it enjoys the different sensory objects through this body. Soul is indestructible & immortal. It moves from one body to the other. As we are not able to see this Soul due to it’s subtle nature so it looks mysterious to us.