addendum

noun3

1. •
   Something to be added; especially text added as an appendix or supplement to a document.

   • An addendum was added to the contract to clarify payment terms.
   • The author included an addendum at the end of the book.
2. •
   A postscript.
3. •
   The height by which the tooth of a gear projects beyond (outside for external, or inside for internal) the standard pitch circle or pitch line.