RE: or "Re:" followed by the subject line of a previous message indicates a "reply" to that message. Otherwise it may also stand for "regarding" a certain subject.

Does re meaning regarding?

Re is defined as an abbreviation for regarding. An example of re is giving a few words at the top of a business letter to say what the letter is about.

Is re the same as regarding?

When written messages were commonly delivered on paper, the term re stood for "regarding" or "in reference to." It was used at the top of a formal letter, followed by the subject of the letter. Re isn't an abbreviation. Rather, it's taken from the Latin in re, which means "in the matter of."