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1.
An informal or personal addition at the end of a letter or note written to a friend, acquaintance, or enemy.

Could also apply to a notation added to the end of scripting or coding in terms of a computer language or semantics.

Common known acronym is P.S.
(contents of note blah blah blah)
Sincerely,
(name here)

P.S. (post script) I had a great time at dinner last night!
by k0nflict June 08, 2009