Souls
Everyone has a soul. It contains a person's entire identity: their self, their memories, their emotions. They are born with them and ideally should stay inside the person's body till death. The soul's color defines the person's eye and ear colors, and, in the case of magicians, the color of their magic.
Souls come in three forms: solid, liquid, and gas.
Everyone is born with a perfectly spherical gas soul. The soul changes shape and form as the person grows, and generally settles in place in their thirties.
Removing souls
A soul can be removed from a person. Soul removal is a skill that can be learned and adopted by anyone, but it originated in Sylvandia.
Through a variety of techniques not limited to classic Sylvandian soul removal (torture is a common example), your soul can come out of your mouth -- commonly known as "barfing out1."
People with no souls aren't people. They're just a body. Their eyes are empty, though their ears, if they have it, would remain in color because pure-white ears look ugly. (It also serves as an indicator of the body's previous ownership.)
Consuming souls
A person can also consume souls. No matter the state, just chug it in your mouth and swallow it.
If there already is a soul (or souls) inside you, the new soul has to merge in. If they aren't compatible enough, it might result in you barfing a soul out.
Compatibility is determined by various factors, like values, life experiences, and what the owners of the respective souls think of each other, but the most important one is its form. Shape is not a factor.
Typically, gas souls are the most compatible with other forms, while solid the least. It would be extremely hard to merge two solid souls together, but other factors, like the owners of the souls being really good friends with each other, may increase compatibility.
