Addendum

[Sarah]

A thing to be added; an appendix or addition. Addendum circle(Mech.), the circle which may be described around a circular spurwheel or gear wheel, touching the crests or tips of the teeth.Rankine.

[Sarah]

Something that is added or later to be added, e.g. a supplement to a book.

[Vania]

An item of additional material, typically omissions, added at the end of a book or other publication.