Well, a bit worrying that anyone thinks the definitive source for this is the preface of a logbook and as some of those definitions (ie PICUS) are hotly disputed on a National level it would behove all student/aspiring pilots to at least know where to look to find out what is applied in their part of the world.
Someone who has got through a PPL training course unaware of the meaning of Dual hasn't been paying attention, but from a Commercial trainee!!!