"ID" or "Id" on User Interface

The 'D' doesn't stand for anything, so I've always considered it an abbreviation, not an acronym - and therefore I too use 'Id', not 'ID'.

I don't know about your qa's reasoning - words can have more than one meaning - this is not unusual in English :)

But it looks like the common usage is actually 'ID' (right or wrong :P), which is probably the format your users would expect.

As an UAUA (ultra-anal usability analyst), please use ID instead of Id.

Visually, it's more recognizable in English. Grammatically, "Id" is a word (rhymes with "squid") and the Freudian definition has been given above. We're never verbally asked to show "id", but "ID." I.D. is fine but passe, as the periods imply multiple words.

So.

Just use ID, okay?

OK.

Personally, I use "Id". The compiler doesn't care but my eyes do. Compare:

GetIDByWhatever  <-- looks terrible

GetIdByWhatever  <-- oh so pretty!

Aesthetics is more important than grammar when it comes to code, always. (Update: 4 years later, I don't stand by this statement anymore)

According to Merriam-Webster, the abbreviation is "ID". If it were a correct abbreviation, it would have to be "Id." with the period.