(especially in business letters) about; on the subject of

Re your communication of 15 February ... 兹就你2月15日来信…

used in the subject line of an email when it is a reply to another email, followed by the subject of the original message

Re: invoice 回复：invoice

the second note of the sol-fa musical scale

used to add the meaning "do again", especially to verbs

rebuild 重建

remarry 再婚

reusable 可重复使用的

returning something to its original state

the regreening of our country (= making it green again by planting trees, allowing grass to grow, etc.) 重新造林

short form of are

You're late. 你迟到了。