P.S. stands for Post-scriptum, latin word for “written after”. In a letter you use it when you forgot to write something and already signed your letter; then you add “P.S. what you forgot”. In simple words, P.S means – By The Way, Just To Let You Know, or Don’t Forget. P.S is like leaving a simple note behind.
https://www.quora.com/What-is-the-meaning-of-P-S-that-people-use-on-Facebook-Quora-etc

