1. A note appended to a letter after the signature
   "She added a brief postscript to mention the time of the meeting";
   - PS
    
2. Textual matter that is added onto a publication; usually at the end
   "She included a brief postscript to explain the delay";
   - addendum, supplement

Derived forms: postscripts

Type of: annotation, matter, notation, note

Part of: back matter, end matter, letter, missive

Encyclopedia: Postscript