adverb
later on; subsequently; in due course
Formal adverb used in announcements, instructions, or business contexts to indicate that something will happen at a later time.
詳細は追ってお知らせします。
Details will be announced later.
日程は追ってご連絡いたします。
We will contact you later regarding the schedule.
conjunction
Dated conjunction used at the end of a letter to add a postscript; now mostly replaced by 追伸.
追って、先日の件について追記します。
P.S. I will add a note about the matter from the other day.
Derived from the verb 追う (おう, 'to follow'), with the conjunctive form 追って (おって) becoming lexicalized as an adverb and conjunction.