PS是英文postscript的缩写，意为“注释， 备注”，常用于信件、文章末尾。
现代英汉综合大辞典postscript
n.
(信末签名后的)再者, 又及; 附言(略作P.S., PS., PS 或 p.s.)
(书等的)附录; 跋, 补遗
[英](新闻广播后的)结束语
现代英汉词典postscript
n.
（信末签名后的）又及，附言，再者 (= P.S.)
（书等的）附录，跋
PS also P.S. American English [countable] postscript
exp. a note written at the end of a letter, adding more information:
She added a PS to say 'hi' to my brother.
Best wishes, Julie. PS Maggie sends her love.
也可以理解为：顺带说一下