A postface is the opposite of a preface, a brief article or explanatory information placed at the end of a book. Postfaces are quite often used in books so that the non-pertinent information will appear at the end of the literary work, and not confuse the reader.
There are at least two authentic examples of postfaces in published works. One can be found in the 1954 book Dalí's Mustache: A Photographic Interview, by Salvador Dalí and Philippe Halsman. While the main body of the work is a collaboration, each author gets a few words to himself, Dalí in the preface and Halsman in the postface. Another occurs in the philosopher Martin Heidegger's essay The Origin of the Work of Art and is further cited in Jacques Derrida's reading of it in The Truth in Painting (1987).