A ghost character, in the bibliographic or scholarly study of texts of dramatic literature, is a term for an inadvertent error committed by the playwright in the act of writing.
As Kristian Smidt put it, they are characters that are "introduced in stage directions or briefly mentioned in dialogue who have no speaking parts and do not otherwise manifest their presence".
[2] The term is used in regard to Elizabethan and Jacobean plays, including the works of William Shakespeare, all of which may have existed in different revisions leading to publication.
Modern versions of Much Ado About Nothing open act 1, scene 1 with the stage direction "Enter Leonato, Governor of Messina, Hero his daughter, and Beatrice his niece, with a Messenger.
[5] As the editors of The Cambridge Shakespeare (1863) put it: "It is impossible to conceive that Hero's mother should have been present during the scenes in which the happiness and honour of her daughter were at issue, without taking a part, or being once referred to.
Porter argues that when Shakespeare dramatised the poem and expanded Mercutio's role, he introduced a brother for him in order to suggest a more fraternal character.