A witch is a person who has the power to effect change by magical means ("witchcraft"). Most of those encountered by Sam and Dean are practitioners of Black Magic - that is, spells used for self-gain or to harm others. In 3.09 Malleus Maleficarum, it is stated that witches get their power from Demons - presumably in exchange for their souls. It is notable that Sam, Dean, and Bobby often use the same spells and rituals, but would not consider themselves witches.
Witches can be extremely long lived. Only two of the witches encountered has been able to be killed by a hunter.
It is revealed that most witches perform their magic through either chanting or placing a hex bag in the general area where their target is at the time of the spell. Witches also use a magical tome known as a Book of Shadows or a Grimoire.
Sam and Dean discover that the witches have unwittingly, been getting their powers from a demon. In return for their powers they give their souls to the demon. The demon whom the coven had sold their souls to, Tammi, stuck around the coven and killed them off when they displeased her. Eventually Tammi is killed by Dean with Ruby's Knife.
The Malleus Maleficarum (Hammer of Witches) is a manual written for witch hunters in the 15th century. It is one of the most famously misogynistic works in European history: the book is a treatise on how women, due to their inferior and carnal natures, are far more susceptible to the Devil's wiles than are men. While the book was very popular, it wasn't necessarily the most influential witch-hunting text: other witch hunters seemed to consider it went a bit too far in its condemnation of women as a group, which limited its usefulness.
Two very old witches - Don Harding and Tracy Davis - begin sacrificing people in order to raise the demon Samhain from Hell. The spell requires "three blood sacrifices over three days, the last before midnight on the final day of the final harvest." The summoning occurs on Halloween, the day on the Celtic calendar where the veil between the living and the dead is thinnest. Once Samhain returns, he can raise other things from Hell, which promises a bloodbath if he can't be stopped. His raising will break one of the The 66 Seals.
To kill their victims the witches use hex bags, filled with rare objects, to perform the sacrifices and a ritual alter for the final phase of the spell. In one hex bag, Sam finds gold thread, an herb supposedly extinct for 200 years, a centuries-old Celtic coin, and the charred finger bone of an infant. At one point in time, one of the witches was at the scene when one victim was killed, so it stands to reason that she was able to perform the spell earlier and activate its power when she wanted.
When they find that they are low on sacrifices, Don decides to kill Tracy to raise Samhain. Sam and Dean burst in, shooting Don and freeing the apparently innocent Tracy. She incapacitates them and completes the ritual. Once raised, Samhain kills Tracy and goes to a cemetery, where he raises zombies and ghosts to attack them. Sam is immune to his powers and manages to exorcise him, sending him back to Hell.
Although he is a stage magician, Charlie gained actual powers from an old sorcerer's Grimoire. He uses Tarot cards to cast a sort of supernatural target onto other magicians so that his best friend Jay would survive fatally wounding tricks - thus transferring the performance knowledge of those who took his place in death. He also reveals that he cast an immortality spell on himself and wants to do the same for his friends Jay and Vernon. He is killed when Jay pickpockets his tarot cards and then stabs himself with a knife.
Patrick is a 900 year old witch who plays poker with people, gambling with years of their life. When he takes 25 years from Bobby, Dean plays and donates 25 of his own years to Bobby, and loses an additional 25.
Lia, Patrick's partner, gives them a reversal spell. As Dean and Bobby undertake to do it, Sam stalls Patrick by playing cards against him. When the spell fails, Dean's life is in the balance as Sam plays for real. Sam finally wins, saving Dean.
Lia tells Patrick she wants to die, having long outlived her daughter, and they play a hand in which she loses all her years.
Dean thinks the deaths of two police officers "seem a little witchy". Sam agrees, but notes that no hex bags or other signs were found. The deaths are later revealed to have been revenge killings using an angelic weapon.
Maggie Stark and Don Stark are witches, possibly of Romanian origin. They have been in a relationship with for over 800 years. Maggie has separated from Don after learning of his affair with Wendy Goodson. In her anger, she is killing people associated with Don through spells aided by placing a magical coin near them. Don strikes back, ruining her charity art auction and killing her best friend. Sam and Dean try to vanquish Maggie using a spell that requires chicken feet, but are unsuccessful because the chicken feet were unrefrigerated. Finally, Maggie and Don reconcile after some relationship advice from Sam and Dean. However, Maggie still tries to kill them, thwarted only by Don retrieving the hex coins from their motel room. Don also saves them from a Leviathan using a spell that appears to paralyze the creature temporarily.
Four years ago, Sam and Dean were informed of a possession by local wiccan Nora Havelock. When they return in the present, when it appears the demon has returned, they find she has a mail-order witch business, though she only traffics in "white magic", herbs and talismans. She has been translating Latin spells in connections the demon, and suggests that they talk to the demon's old host Jeffrey. Jeffrey, however, is the real culprit in a series of murders, and has been forcing Nora to help him bring back his demon. He kidnapped her son, so she gave him a summoning spell; it failed, and he sent her the ear of her son. She found a stronger spell, one requiring the blood of the demon's exorcist: Dean. Sam convinces her that they must find Dean to save her son, and Nora uses a tracking spell to locate them. By the time they get there, the demon has been summoned and is possessing her son. Sam manages to lure it into a Devil's Trap and Nora exorcises it, saving her son while Dean kills Jeffery.
In order to make "demon bombs," based on instructions from the tablet about demons, Linda Tran hires Delta Mendota from Craigslist in order to get all of the ingredients they need. She informs Delta of what they are trying to make, but not how to make them or the amount of ingredients needed for each. Delta gets the needed ingredients, but frustrated with the way Linda is treating her, she tells Crowley where to find Linda and her son the Prophet Kevin. Delta brings some of the ingredients, enough for at least one bomb, but claims she won't bring any more until she is paid. Upon arrival, Linda squirts her with holy water to prove that she is not possessed. Using an excuse, Delta gets Kevin, who is attracted to her, to let her go into the backroom where she breaks the salt line there so the demons can get in. Kevin discovers this when he goes to get his mother's purse and the demons arrive. Crowley, annoyed with Delta's attitude, snaps his fingers and sends her away somewhere.
After helping Sam and Dean with a case years before, St. Louis police officer James Frampton becomes a witch and uses his magic to help him on the job. However, he gets dreams of and finds evidence of him commiting the brutal murders of four innocent people and his familiar Portia calls in Sam and Dean to help as James doesn't trust anyone in the witch community. Sam and Dean are unhappy due to their previous encounters with witches, but agree to look into it before killing James. They eventually find a spell in Bobby Singer's files that a witch could use to implant a false memory in another witch, but are unsure that James is innocent as all evidence points to his guilt. However, James and Portia are in a relationship and while having sex, Portia sees into James' mind and sees that all he remembers is actually commiting the act with no preperations or motive to do it. Dean and Portia also learn that the witch community plans to force James to either leave or kill himself to avoid exposing them. Realizing that police detective Ed Stoltz is hiding something, Sam, Dean and James use astral projection to visit the police station where they learn that Stoltz is building a case against James using James' friend Spencer's familiar Phillippe LeChat as a witness. James confronts Phillippe who tells him that he was framing him under Spencer's orders. Spencer kills Phillippe and reveals that he is framing James because he is jealous of James' relationship with Portia who he had wanted as his own familiar. James engages Spencer in battle, but is no match for him and when Sam and Dean try to intervene, Spencer makes them relive horrible memories. However, Portia attacks Spencer, freeing Sam and Dean who kill Spencer with a witch-killing spell Bobby taught them. James and Portia then leave town to start a new life together, knowing Ed has too good of a case against them and that the witches in St. Louis never really accepted them.
Witches in real life and lore
The term witch in its broadest sense refers to a person who claims to tap into some form of supernatural power. These people exists in cultures around the world, and may take the role of a healer or wise person in a community. Their powers could be used for either good or harm. The modern use of the term and its associations are rooted in the pogroms of the Middle Ages, against people, particularly women, who practiced any form of belief or healing that could be deemed anti-Christian. During these witch hunts in Europe and later North America, tens of thousands of people were tortured and killed based on the justification that they were in league with Satan.
In the 20th and 21st century, people who follow a form of Neopaganism may refer to themselves as witches. The most well known of these is Wicca, which originated in the 1930s, although its beliefs are formed on older pagan cultures such as those of the Celts and the Greeks. The religion involves the ritual practice of magic.