The soul is the entirety of our individual entity, i.e. the totality of our consciousness. We are multidimensional beings and hence we exist on many levels including this portion of our current personality on the earth plane. This includes all our incarnations and also the other parts of us which are not.
Kryon (channeled by Lee Carroll) explains:
The soul is often seen as the overview of all that you are. It includes all the "selves" that you have, including the ones that aren’t here in 4D. Therefore, it’s a name that would indicate a "divine wholeness," and is often meant to reflect the "entire system of you." This would include the "I AM" presence you have in the Universe.
All human beings have a soul, as explained by Kryon (channeled by Lee Carroll) as follow:
Can the Human body exist or live productively without the presence of a spirit or soul?
ANSWER: No. Even the most seemingly uncaring or evil Human, or the one who is brain-dead or insane, has a soul and an essence of divinity. It’s all part of a combination of free choice and that of fulfilling specific energies for the benefit of creating balance (or the lack of it), which helps the rest of you make important decisions about your own divinity.
Source http://kryon.com/inspiritmag/archives/Q-A%20archives/2004-Q%26A/Q%26A-1rstquarter04.html#25
