The religious definition of the soul is:-
Soul is defined as one person, or is the spirit and essence of a person. An example of your soul is the part of you that makes you who you are and that will live on after your death. An example of soul is the part of you that will go to heaven and be immortal, according to the the teachings of certain religions.
There is of course not one shred of evidence to back up that statement.
I don't know of a non-religious definition.