abbreviations - Which one is correct: Id or ID? - English Language . . . Commented Feb 6, 2016 at 19:54 1 @FumbleFingers - Let me agree that "ID" is short form of "Identity Document" But, we find a commonplace thing, such as, "What is your email ID" or "What is your email id" Obviously, the speaker is asking for "email Identity" or "email Identifier" and not for "email Identity Document" or email Identity Card"