It is an abbreviation for Post Script It basically started when one would begin writing a letter, sign it and then remember that they wanted to add something to the letter. Such as: Hi! How are you doing? It is very cold here. I look forward to seeing you. Love, (name) P.S. Did you get the cookies I sent you?

It comes from the Latin phrase post scriptum (always written in capital letters as P.S.) wherein post means after and scriptum refers to the written text. P.S. tells (or signals) to the reader of the letter that the text that the abbreviation P.S. comes before were written at a different time that the letter above. P.S. Good Luck with your studies!

it means " post .script " to add anything you forgot to mention in your letter

It is PS or P.S. (no dots or two dots). If you wanted to add more notes, you can add another P (PPS, PPPS, etc.)