A soul or spirit is a non-physical entity capable of perception and self-awareness. Souls are often believed to be immortal.
If ever there were an entity invented for human wish-fulfillment, the soul is that entity. As Thomas Hobbes pointed out, the concept of a non-substantial substance is a contradiction. It is not possible to imagine a non-physical entity having life and perception. Even believers in souls always imagine them as being like human shaped clouds or fogs. It is a delusion to believe that the concept of soul is conceivable. Yet, billions of people have believed in a non-spatial perceiver which can travel through space and perceive and interpret vibrations and waves in the air without any sense organs.
Work done by philosophers and psychologists based on the assumption of a non-physical entity, which somehow inhabits and interacts with the human body, has not furthered human understanding of the working of the mind. Instead, it has furthered superstition and ignorance while hindering the development of any real and useful knowledge about the human mind. More promising is the work of those who see consciousness in terms of brain functioning and who try to treat 'mental' illness as primarily a physical problem. Two vast industries have been made both possible and lucrative by this belief in a non-entity in need of treatment from experts in non-entities: religion and psychology. A third industry, philosophy, also flourishes in great part due to the concept of soul: a good many philosophers write books and articles based on the assumption of the existence of spirits, while a good many others make a living writing refutations and criticisms of those books and articles. It seems that the skeptic and the true believer need each other!