Throughout the months I have been reading Ac.SE I have come across questions where the context of the question in a way depends on some abbreviation which is not explicitly defined. I realise that some abbreviations have become common knowledge (e.g. PhD, CS..) but some others might be ambiguous to many.
In publications one is often required to "introduce" any abbreviation that recurs, and I suppose it would not be too much to expect the same here.
What do you think? Is there an "official policy" on this matter?