The noun soul can mean an individual human being, but it can also mean essence of a human being. If you believe the soul is immortal, you believe that even when your physical body dies, some other part of you lives on.
Soul shows up in various forms in all Nordic and Germanic languages, but no one knows where it originated, just like the whole idea of the soul. Philosophers and theologians have debated the exact definition of soul for ages, but it always stands for that ineffable part of a human unlimited by the body, the grandest, deepest part. Soul music is a popular form of gospel, and if you "have soul," you really feel what it is to be alive.