The soul is the totality of qualia making up a person.
This definition is meant as a theorem. For a theory on consciousness, a definition of 'soul' is not strictly necessary (doing without, one may say, is to yield the Bhuddist way). When things need to be restricted to the essentials the term could be done away with. Yet it in practice does need to be defined in order to be able to deal with texts and reasonings in which the term is used and meaningful. The soul therefore is usually conceived of as being something like the essence or core of a particular human being. But as such, it's existence cannot definitely be pointed out.
People are inclined to doubt the validity of the term because of the clear non-objectifiabilitty of the soul and the wish to be 'scientifically pure'. That's why I choose my definition as above, for by this, the term is to literally get a true body!
To conceive it like this, I make use of the materials on lifes of disembodied spirits that are around. It is generally assumed that the non-physical realities need not be that dramatically different from the physical at all - it is the physical reality that is truly strange, as within physical reality qualia always have to be expressed in some physical substratum, such as your body.