Well, according to someone I know (in real life, no, not a teacher) who has a degree in History (masters) 'D' does not actually stand for anything, although there are various words that have been put in its place, and which have become so popular that people now actually believe it's so. It's like the whole "Tomatoes are fruit, not vegetables" thing - a lot of people don't realise tomatoes are fruit, because everyone puts them in with vegetables, i.e. salad.
Oh, by the way, my History teacher ALSO said that the 'D' stands for nothing, but he only has an A-level in the subject
(or whatever they had 27 years ago)
Regards,
