The abbreviation P.S. is short for the Latin post scriptum, meaning "after what has been written".
It is used after the end of a letter to indicate a last-minute addition.
a.m. & p.m., cf., e.g., et al., etc., i.e., N.B., P.S., Q.E.D., q.v., viz.
ad hoc, de facto, modus operandi, non sequitur, pro rata, quid pro quo, sic, vice versa.