Widely linked to magic, crossroads are said to be haunted by various entities who take joy in confusing travelers. Visited by ghosts, activities of demons, the Devil, witches and fairies, the meeting and parting of ways can also be used to conjure up the same spirits who appear there. Also, the shape of the crossroads can be used in protection against these. Spirits appear at crossroads every All Hallow's Eve and at other times, can be conjured up to appear there. Also, the very shape of crossroads is in some lore protection against the spirits alleged to haunt the places.
Crossroads are where pacts are made. These people are actually making deals with the damn thing. You know, 'cause that always ends good.
In 2.08 Crossroad Blues, Dean describes the spell used to summon a crossroads demon as "deep south hoodoo stuff." The ritual involves burying a container holding graveyard dirt, a bone of a black cat, and a photo of yourself at a crossroads.