Soul

A soul is a person's essence, and what persists after death. In Supernatural, a soul separate from its body is visualized as a blinding white light.^{5.14 My Bloody Valentine}

After Death

Most spirits are transported by reapers after death to the next destination. Those who refuse to move on can become ghosts or vengeful spirits

Hell

Demons are formed in Hell by the corruption of a human soul over time. Lucifer made Lilith into the first demon in order to mock God's creation of humanity. While in Hell, Dean eventually broke under Alastair's torture and started torturing souls himself, and so likely would have been transformed without Castiel's intervention.

Heaven

In Heaven, each soul has its own version of Heaven where he or she relives happy memories. Heavens are individual, except in the case of soulmates, who share the same Heaven, according to Ash. Most souls cannot leave their own allotted space.^{5.16 Dark Side Of The Moon}.

Purgatory

Purgatory is a spiritual realm where the souls of supernatural creatures go after they die. This place is not connected with Heaven or Hell, though it has been referred to as "hell adjacent".

After resurrecting Samuel Campbell, Crowley has him tracking down high-ranking creatures, especially Alphas, so that he can question them about the location of Purgatory, which he wants for "development purposes."

Deals and Markers

Souls are first mentioned explicitly in Supernatural in relation to the deals made by Crossroads Demons, wherein a person agrees to give their soul to the demon upon death in exchange for some benefit when they are alive. Crowley was originally the head Crossroads Demon. The deals are traditionally sealed with a kiss, and have a set time limit at the end of which the subject of a deal, if still living, is killed.

John Winchester sold his soul to Azazel in exchange for Dean's life ^{2.01 In My Time Of Dying}, and Dean did the same for Sam.^{3.16 No Rest For The Wicked} Sam attempted to sell his own soul to bring back Dean, but was refused.^{4.09 I Know What You Did Last Summer} Bobby sells his soul to Crowley to get information on Death's whereabouts in order to help stop the Apocalypse. The deal is undone when Bobby, with help from Sam and Dean, threatened to destroy Crowley by burning his bones.^{6.04 Weekend At Bobby's}

See the Crossroads Demon entry for a list of deals made.

Balthazar bought the soul of a boy, Aaron Birch, in exchange for a part of the Staff of Moses. It is unclear why he wants the soul, though he refers to souls as the only thing left of value, and he is eventually forced to return it.^{6.03 The Third Man}

In claiming Aaron's soul, Balthazar left an identifying mark on it. Castiel has the ability to 'read' a person's soul, and sees the mark of the other angel when he reads Aaron. Castiel can also identify the absence of a soul, and is therefore able to determine Sam's soulless state in 6.07 Family Matters. crowley is also able to make the details of the contract he made with Bobby manifest as writing on his skin.^{6.04 Weekend At Bobby's}

Famine

In 5.14 My Bloody Valentine, the Horseman Famine sends a demon to retrieve a soul for him to feast on, and the demon transports the soul in a briefcase. The demon is killed by Sam, who, upon inspecting the briefcase with Dean, releases the soul, which appears as a brief flash of light.

Sam's Soul

Castiel: Somehow, when Sam was resurrected, it was without his soul. Dean: So where is it? Castiel: My guess is still in the cage with Michael and Lucifer. Dean: So is he even still Sam? Castiel: Well, you pose an interesting philosophical question. – Castiel and Dean, 6.07 Family Matters

Castiel ascertains that the reason Sam is feeling no emotion, and no longer sleeps, is that he was resurrected without his soul.^{6.07 Family Matters} Sam is the first human known to be living and soulless, as demonic deals usually leave the soul intact until death.

Crowley claims that he pulled Sam out of Lucifer's Cage, but kept the soul back, and that he will return Sam's soul if the Winchesters help him find Purgatory - a task he has had Samuel Campbell working on since his resurrection.

Souls in Religion and Lore

• The key events in the 1.01 Pilot - the night when Sam is fed Demon Blood by Azazel, and Mary dies, and also the night Jessica dies - occur on November the second which is known as All Souls Day.
• The soul in religion and philosophy from the Catholic Encylopedia
• Wikipedia entry on souls.