What does the re: in email subjects stand for?

According to this page on an online Latin dictionary site, RE is a Latin word.

It means -- Respecting; in reference to. For example "re Brown" means in reference to the case of Brown.

I don't know if email's use of RE is Latin. Like you, I've always thought it was a shortcut for REgarding. But the Latin word definitely fits, based on the definition. 8-)

ah, sorry, I think mdy's answer is professional. but could we think it by another way and just simply it? for example, the "re" could stand for reply, response, re-email to,,, someting like that?

The idea is that the first e-mail's subject was the original question, and the second e-mail's subject is "Re" the first one. So looking down your list of e-mails, you have one labeled "Wiget Orders are Up this Quarter" and a second one labeled "RE: Wiget Orders are Up this Quarter".

My guess is that mdy and stephenzai are both right -- it started with the formal "RE" (like on a memo's subject line) but became simply "In REply to"

Anecdotally, on IRC waaay back in 1993 or so, there was a construct where when someone left and came back, you could greet them with "re" -- in that case short for "rehi", or Hi, again.

Prior to e-mail, RE: was used in letters to mean either Regarding or Reference (this was usually legal based i.e. RE: Case 2007-345). But like a lot of things I think the meaning has been adapted to modern communication and Regarding is probably the most accepted association for RE:

i always thought reply myself

I concur with Quandry;
I always thought it was "REgarding" or "in REference to" from the old Re: in memos
(perhaps we're dating ourselves!)