Very broadly, a paratext is everything that surrounds a text that is not necessarily part of the text’s primary content. It is a literary concept discussed by Gerard Genette in Paratexts: Thesholds of Interpretation. In the Introduction to his book, Genette describes the paratext as “a threshold…that offers the world at large the possibility of either stepping inside [a text] or turning back” (2). It is “what enables a text to become a book and to be offered as such to its readers and, more generally, to the public” (1). Paratexts bring the reader into a text and influence their reception of it.
Examples of paratexts include: a title, an author’s name, a dedication, a preface, notes, illustrations, interviews, a prospectus, a biographical notes, private communications (such as letters or journal entries), the “material existence” of the text (typographical choices; how the text is bound or if it is an e-text), and factual elements (which can range from knowledge of the author’s age to socio-cultural/historical knowledge of the time in which the work was produced).
Source: Genette, Gerard. Paratexts: Thresholds of Interpretation. Trans. Jane E. Lewin. Cambridge: Cambridge UP, 1997.