Tbh, I don't really know what the soul is. I believe it is some sort of invisible thing that processes/carries information, and carries over from one incarnation to the next. It is also our connection to 'source". AkuManiMani said that the soul is the combined motivations and preferences that make up a person, but I believe this has more to do with Fi. The soul I think actually is linked to Ni. Wish I had a better answer but if I'd had discovered what the soul was exactly I would probably have won the Nobel price (or maybe not, given the decline of spirituality of the present age).