I find the people using both:

"Id" and "ID"

I do not know which one is correct.

To me, the 1st one ("Id") is correct, as "Id" and "ID" are abbreviations of "identifier". The correct one is "Id". "ID" appears to be an acronym of two words, though there is only one word, "identifier".

Can anyone please shed some light on the issue?

  • ID can be a shortened form of other words/phrases besides identifier. For example, "ID" can be a shortened form of identification card (e.g., "May I see an ID, please?"), or even the verb identify (as in, "The victim was able to ID the robbery suspect").
    – J.R.
    Feb 6, 2016 at 18:24
  • I imagine lots of people capitalize both letters because id is a word in its own right, and in many fonts, the lower-case version of L is identical (or easily confused with) the upper-case version of i. It's such a short abbreviation it's not going to seriously distract the reader if it's written entirely in upper case, and it's important to note that in many/most contexts it's actually pronounced as "eye-dee", so it just seems natural to write it as if it's two letters. The question "Which one is correct?" is practically impossible to answer. Feb 6, 2016 at 18:25
  • 1
    Is your context ordinary writing, where it is OK to have abbreviations that consist of multiple capital letters in a row? Or is your context computer programming, where camelCaseIdentifiers and CapitalizedCamelCaseIdentifiers are common?
    – Jasper
    Feb 6, 2016 at 18:37
  • Definitions of id Looks like ID wins. I have never seen it written differently. (AmE)
    – user3169
    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". To me, "id" or "ID" is short form of "Identity" or "identifier". But, I am not sure. One more thing, this is not a general reference. I did not find this in Collins dictionary (Indian Reprint 1991) I use. That is why, I posted this question. But, I am surprised that it is "on hold".
    – Kirti
    Feb 7, 2016 at 17:57


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