re

剑桥词典

formal
(especially in business letters ) about; on the subject of
（尤用於商務信函中）關於，玆就，事涉
Re your communication of 15 February ... 玆就你2月15日來信…

used in the subject line of an email when it is a reply to another email , followed by the subject of the original message
（用於廻複電子郵件時的標題行，在被廻複的郵件的標題之前）
Re: invoice 廻複：invoice 返回 re