A postscript is something added to a letter after the main message has been finished and signed. Writers mark it with the letters P.S., which stand for the Latin phrase post scriptum, meaning “written after.”

When you realize you forgot to mention something important in your letter, you can add a postscript below your signature instead of rewriting the entire thing. For example, you might write P.S. Don't forget to bring your soccer cleats! at the bottom of a letter to your cousin. Sometimes people use postscripts to add a lighthearted comment or personal touch: P.S. Mom says hi!

Before email and text messages made it easy to edit what you'd written, postscripts were especially useful. Once you'd written a letter by hand, adding a P.S. was much simpler than starting over. Today, people still use postscripts in emails and even texts to add an afterthought or emphasize something they don't want the reader to miss.

The word can also describe anything added after the main part is complete. A book might include a postscript chapter explaining what happened to the characters years later, or a speaker might offer a postscript to their presentation with updated information.