A soul is an essence of a being that is incorporeal and often a representation of who they are, or were, in life. Souls are often released into the afterlife of a person's belief. Not everyone has a soul, depending on their beliefs. Some are able to use their own souls, such as Æon Knights, while there are other creatures that consume souls, including some demons like Memnoch.
The size of a person does not dictate the scope of the soul, which grows or shrinks depending on the individual's character[Tales 1]. Some souls, such as animal souls or cloned souls, will not be as strong as a long-lived soul of a sentient being[Tales 2].
For many, their soul journeys to the afterlife they believe in upon their deaths. Some, however, may be forcibly sent somewhere, or even given up to a soul-eater[Tales 1].
See also: Memnoch
Memnoch, the Archdevil of Tartarus, consumes trillions and trillions of souls. He was given a microuniverse by Ameryl Hypericum, which would allow him to consume all souls within it every Earth day[Tales 1].