- Harry Potter: "Where are we, exactly?"
- Albus Dumbledore: "Well, I was going to ask you that. Where would you say that we are?"
- Harry Potter: "It looks like King's Cross station. Except a lot cleaner and empty, and there are no trains as far as I can see."
- — Harry Potter finds himself in Limbo.[src]
Limbo is a state of being that exists between life and death. Limbo comes to being inside a person's mind making it both real and unreal. Its appearance is different for each person who visits it. Some Limbo experiences involve loved ones or acquaintances. 
In May of 1998, Harry Potter allowed himself to be struck by a Killing Curse cast by Lord Voldemort in an attempt to protect his friends and loved ones and to destroy the piece of Voldemort's soul that resided within him. What neither he nor Voldemort realised, however, was that when Voldemort used Harry's blood in his resurrection in 1995, he unwittingly took Lily Potter's magical protection of Harry into himself as well, thereby tethering Harry's life to his own.
Harry awoke to find himself lying naked in a formless mist. As he adjusted to his surroundings, he wished to himself that he were clothed, and as this wish came to him a short ways away a pile of clean fresh clothes appeared. After putting the clothes on, the mist began to take shape into a copy of King's Cross Station, Harry saw a stunted, whimpering child-like form lying on the ground, for which he felt both pity and revulsion. He also saw Albus Dumbledore, his deceased mentor, and the two had a long talk in which Dumbledore answered many of Harry's questions and told him that he wasn't actually dead. As a soul that was whole and complete, Harry was given the choice to return to the world of the living to finally stop Voldemort, or to board a train and "go on". Harry chose to return, and when he stood against Voldemort in Hogwarts's Great Hall, Harry warned him that he had seen what fate awaited Riddle when he finally died, unless he were to attempt to mend his broken soul through remorse. Voldemort, being ignorant of such fate and the importance of his soul's well-being, as well as arrogantly believing that he won't die, ignored the warning and proceeded to attack.
With the destruction of all of his Horcruxes, when Voldemort's Killing Curse rebounded and finally ended his life once and for all, his broken and mangled soul was forced to exist in the stunted form Harry saw in King's Cross, unable to move on or return as a ghost, nor does it have any chance of repairing itself any further or be helped by anyone in any way.
In Dante Alighieri's Inferno, Limbo is the first circle of Hell. It's where pagans who were good people go, because they didn't believe in the Judeo-Christian God. The word itself derives from the Latin word, limbus, meaning "edge, border". So Latin "in limbo" came to mean "in a condition of neglect or oblivion". The word is entirely unrelated to the Muggle dancing game, limbo, which derives from West Indian roots (same as "limber").
Behind the scenes
- It's not specified if all souls of the dead pass through Limbo before moving on, or if Harry's visit there was due to the unique circumstances that tethered both Voldemort and himself to life.
- During the third task of the Triwizard Tournament in the 1994–1995 school year, a Limbo Mist was used as an obstacle.
- When Graham Montague was trapped in the broken Vanishing Cabinet, he was described as being in limbo. However, that term doesn't refer to this place, but rather being stuck between Hogwarts Castle and Borgin and Burkes, unable to pass into either.
- In Harry Potter and the Deathly Hallows: Part 2, Harry wakes up in Limbo in his clothes (different clothes, however, to the ones he was wearing in the Forbidden Forest) rather than being naked like in the book. This was likely done for censorship reasons.
- It's unknown if the mangled form of Voldemort's soul was a standard fate that all Horcrux creators (such as Herpo the Foul) were given at death, or it was unique in Voldemort's case, given the nature of his many crimes over his lifetime and the creation of more Horcruxes than anyone else.
- In Harry Potter and the Deathly Hallows: Part 2, Voldemort's soul in Limbo greatly resembles the rudimentary body that Voldemort used during the film version of Goblet of Fire. Whether this is a coincidence or intentional on the filmmakers' part is unknown. Though based on the description in the fourth and seventh novels, the appearance of Voldemort's stunned form does match.
- Seeing that a ghost takes on the form of the wizard/witch's appearance at the time of death, it's most likely that Voldemort's soul is indeed a reflection of his rudimentary form.
- It's possible that Limbo is the place at which a recently–deceased person can make the decision whether to move on or return to the mortal world as a ghost.
- Harry Potter and the Deathly Hallows (First appearance)
- Harry Potter and the Deathly Hallows: Part 2
- Harry Potter and the Deathly Hallows: Part 2 (video game)
- LEGO Harry Potter: Years 5-7