An afterword is a literary device that is often found at the end of a piece of literature

Literature

Literature is the art of written works, and is not bound to published sources...

. It generally covers the story of how the book came into being, or of how the idea for the book was developed.

Alternatively, it may be written by someone other than the author

Author

An author is broadly defined as "the person who originates or gives existence to anything" and that authorship determines responsibility for what is created. Narrowly defined, an author is the originator of any written work.-Legal significance:...

of the book to provide enriching comment, such as discussing the work's historical or cultural context (especially if the work is being reissued many years after its original publication).