What do you believe "the soul" is?

Tsubasa Hanekawa! Are you watching Monogatari by any chance?

Anyways a person's soul is their spiritual being,personality,everything that makes an individual an individual.

It's unlike any other souls. Human soul I believe it's phenomenal.

Our essential and spiritual selves that live on after the physical self doesn't.

"Soul music (often referred to simply as soul) is a popular music genre that originated in the United States in the late 1950s and early 1960s. It combines elements of African-American gospel music, rhythm and blues and jazz."

The Soul is one's spiritual essence. It is a representation of our true selves and everything that defines us. In a way, I believe that they are also our real forms that await to be set free once our Physical Bodies have fulfilled their purpose. The later is only a temporary vessel. It serves the same purpose as a Butterfly's Pupa Stage, for example (Ever heard of the Chrysalis? That is exactly it). What is released after might be entirely different from what someone would assume at first. Regardless, it will take shape based on the qualities that we hold dear inside. A certain Image will be formed. One that is clear and devoid of imperfections. Of course, each Soul varies just like every living being in general. That uniqueness is what makes them special though. That is Perfection in itself !!!!

Something that only exists in people's heads

Not to say that I don't believe in it, but it's more like a cognitive essence, or the idea of a person rather than the physical makeup of a person