The soul seems to be a part of a human that was there before one was born, and won’t die when one dies… an eternal aspect of a human.
A soul – in certain spiritual, philosophical, and psychological traditions – is the incorporeal essence of a person or living thing or object. Many philosophical and spiritual systems still teach that humans have souls, and others teach that all living things and even inanimate objects (such as rivers) have souls. The latter belief is commonly called animism. Soul can function as a synonym for spirit, mind or self.
Although the terms soul and spirit are sometimes used interchangeably, soul may denote a more worldly and less transcendent aspect of a person. According to psychologist James Hillman, soul has an affinity for negative thoughts and images, whereas spirit seeks to rise above the entanglements of life and death. The words soul and psyche can also be treated synonymously, although psyche has more physical connotations, whereas soul is connected more closely to spirituality and religion.
According to Kabbalah, depending on which “plane” you observe the soul, it is different, nefesh, neshama, etc. are different words to indicate that. I am not an expert at that…